87 = 56
155 = 75

56 - 4 + 75 - 4 = 123

3 - 2*5 = -7
-7 + 3 = -4
-4 - 6 = -10

6*5 = 30
30 - 4 + 5 = 31
31 - 6 = 25

Therefore, the final result is:
123 - 10 + 25 = 138