Question 1200692
j = john's age.
b = his brother's age.
j = 5b
j - b = 12
replace j with 5 b in the second equation to get:
5b - b = 12
combine like terms to get:
4b = 12
solve for b  to get:
b = 12/4 = 3
j = 5b gets you j = 15
j - b = 12 gets you j - 3 = 12 which gets you j = 3 + 12 which gets you j = 15 again.
your solution is that john is 15 and his brother is 3.