Question 791641
The difference of the ages of two boys A and B
A - B = 3
sum of their ages is 27.
A + B = 27
.......
A + B = 27
A - B = 3
Add together
2A    = 30
A = 15
Substitute A = 15 into;
A + B = 27
15 + B = 27
B = 27 - 15
B = 12
A is 15 years old
B is 12 years old.
Hope this helps.
:-)