Need to be careful here
f-1 (-3) means that either
2 - x = - 3
x = 5 but this value isn't in the domain of the first function
or
2x - x^2 = -3 rearrange as
x^2 - 2x - 3 = 0 factor
(x- 3) ( x + 1) = 0
x = 3 or x = -1
Only the first value is in the domain of the second function
So... f-1(-3) = 3
Likewise
f-1(0) means that either
2 - x = 0
x = 2 not in the domain for the first function
or
2x - x^2 = 0 factor
x (2 - x) = 0
x = 0 or x = 2
Only the second value is in the domain of the second function
So ...f-1(0) = 2
Lastly
f-1(3) means that
2 - x = 3
x = -1
This value is in the domain of the first function
So....f-1 (3) = -1
So
f-1(-3) + f-1(0) + f-1 (3) = 3 + 2 + -1 = 4