for fun

Yes, but we can define the equation which defines all solutions to this problem.

If we add both equations we have

sf+sp = 14+21

s(f+p) = 35

This is part of the surface the equation desribes.

Reinout 

This can't be precisely determined because we have more equations than variables.

For example .....s could be 7, p could be 3, and f could be 2

Or.....s could be 7/2 , p could be 6, and f could be 4

This will always be the case for a system when we have more variables than equations......we will have an infinite number of solutions  (I believe that this is known as an "underdetermined" system)