Answer = 37.
If you analyse the equations properly, you will find the connection between the numbers to be as follows;
The result is equal to the difference of the middle digit in the first number plus the the second number which is 0 is addition of the other 2 digits in the first number.
238 + 0 = 20 => 30 – (8 + 2) = 30 – 10 = 20
329 + 0 = 8 => 20 – (9 + 3) = 20 – 12 = 8
637 + 0 = 17 => 30 – (7 + 6) = 30 – 13 = 17
Therefore last equation will be;
458 + 0 => 50 – (8 + 4) = 50 – 13 = 37
I cheated... Ctrl+C, Ctrl+V... downvote if optional.