Assuming that most Christians--if not a vast majority of Christians, regardless of denominations--consider the Bible to be at least somewhat authoritative in faith and practice, I suggest you read the verse in question in context to arrive at a partial answer, if not the answer.
On more than one occasion Jesus used threes (3's) in his teaching. In the passage to which you refer, the three righteous deeds he cites are giving (vv.1-4), praying (vv.5-15), and fasting (vv.16-18). In each case Jesus gives his followers a negative example preceded by the words "beware" or "do not." He then ends the negative example with the words
"they have their reward in full" (vv.2, 5, and 16).
He then gives them a positive instruction, each time preceded by the word but:
But when you give (v.3)
But you, when you pray (v.6)
But you, when you fast (v.17)
At the end of each positive instruction, Jesus ends with the words
- Your Father will reward you (vv.4, 6, and 18)
Putting these bits and pieces together, I think we are safe in thinking that Jesus was contrasting the short view with the long view, temporal rewards with eternal rewards, and self-centered religion with God-centered religion.
Religionists with the short view want their reward now, and their righteous deeds are primarily self-centered.
In a show-off religion, the goal for those practitioners who give, pray, and fast, is to be noticed, praised, and to be well thought of by people. Jesus asserts their obvious and public giving, praying, and fasting are self-centered and are neither others-centered nor God-centered.
In Jesus' kingdom, true religion begins first with a personal and intensely private love relationship with a heavenly Father. Out of that relationship flow good works such as giving, praying, and fasting. Put differently, Christians first love God supremely (with heart, soul, mind, and strength--the "first and greatest commandment"), and then out of the overflow of their vertical relationship with God they are enabled to love their neighbors as themselves in those horizontal relationships (the second great commandment).
Putting all the above pieces together, then, I think it safe to say that Jesus' teaching is that the heavenly Father's reward for each righteous deed, when it is done in secret, is his good pleasure.
We need look no further than the relationship between a child and a parent. When the child obeys the mother or father in performing a task such as mowing the lawn, taking out the garbage, or cleaning a messy room, the parent cannot give a greater reward to the child than a sincere
Well done, Sally. You did a good job!
"Good job, Johnny. I'm so proud of you!
Regarding your specific question about whether God's reward for secret prayer comprises--at least in part--answers to those prayers, my answer is a definite yes, particularly his children pray for God's will to be done. In those secret times of prayer, when Christians pour out their hearts to God, God not only hears but he answers. The answers may not always be the ones his children want, but when they ask in faith according to his will, he assures them he will act.