We have two numbers say a, b. And a system of equations.

It looks a bit intimidating but it's actually very easy.
Instead of term a + b in the second equation we can say it's zero because the first equation describes a + b as being equal to 0.
So,

The above equation is not true therefore numbers a and b do not exists in the real number domain.

No solution.
Hope this helps.
C = 2 pi r
C = 2 x 3 x 2
C = 12 units
answer
A. 12 units
Ok so you have to replace all x by 4:
F(4)= 4.4+7= 23