You need to isolate the variable my dividing each side by factors that don’t contain the variable
x=-5
Answer:
-$173
Step-by-step explanation:

m = 4b+3 mikes age
m +b <138 mike +brother less than 138
4b+3+b<138
5b +3< 138
b< 135
b <27
The oldest the brother can be is 26