So for these types of questions you want to substitute the value given into the equation...
So for a,
f(x)=2x-7
f(-3)=?
well instead of x you place -3,
so
f(-3)= 2*-3 - 7
So now you solve using order of operations (PEMDAS)
So,
2*-3=-6 So,
f(-3)=-6-7
-6-7=-13
So,
f(-3)=-13
Try to do that for the others and I'll let you know if you're right. Good luck!