Find the value of c when a=1 and b=7?

I have this on Kumon and can't figure it out!

There must be more to the question. So far, you haven't told us

anything about how 'c' depends on 'a' and 'b'. So, using just the

information given in the question, no answer is possible.

The question is a lot like asking:

"Find how long I sleep when

my dog rolls over and my wife eats oatmeal."

I'm probably wrong but maybe 13 or 49 because there are 2 possible patterns: add 6 or multiply by 7.

This is the only possible answer I can think of, sorry if I'm wrong.