You want to find "a" when f(2) +f(3) = f(5), for f(x) = 2x^2 +a.
Substituting, we have
... (2·2^2 +a) + (2·3^2 +a) = 2·5^2 +a
... 8 + a + 18 + a = 50 + a
... 26 + a = 50 . . . . . . . . . . . subtract a
... a = 24 . . . . . . . . . . . . . . . subtract 26
The appropriate choice is
... C) 24
