Can you identify the logic behind the equation below and solve the puzzle by completing the equation?

12 + 13 + 7 = 1
15 + 16 + 11= 2
17 + 18 + 16 = ?

4

Logic Used: Sum the numbers and then subtract the two digits to get the desired answer.

12 + 13 + 7 => 32 => 3 - 2 => 1
15 + 16 + 11 =>42 => 4 -2 => 2
17 + 18 + 16 = 51 => 5 -1 => 4