Please help me. i will mark if correct xo.

I’m going to try my best so I apologize if this is incorrect

function: f(3) = 15x- 40
solution: 5
15 • 3 = 45
45 - 40 = 5

function: f(21) = 2/3x + 20
solution: 34
2/3 • 21 = 14
14 + 20 = 33

function: f(-2) = (3x)^2 + 17
solution: 53
[3(-2)]^2 = 36
36 + 17 = 53

again I apologize if this is incorrect

Whose mistake? can you give more details to what the question is asking?