Given the question as written, a=7, b=-10, c=98.

I've seen this problem before used to teach a number of common families of equations, and if they are not the equations given by your teacher, then I suggest that you ask for clarification. The equations I've seen in the context of this "birthday problem" are as follows:

1.) a^3 - b^3 (this is called the difference of cubes, and can be expanded, as shown in the following line)

=(a-b)*(a^3+ab+b^3)

= (17)*(343-70-1000)

2.) b-c

=-10-98

=-98

3.) 2b-a

=2(-10)-7

=-27

Note: the caret symbol (^) is used to represent an exponent.