Question 1128059
I assume you mean 3 more than twice his brother's age instead of 3 times more.
Let x = the younger brother's age, y = John's age
y = 3 + 2x -> x = y/2 - 3/2
x + y <= 18 y <= 18 - x -> y <= 18 - y/2 + 3/2
Solve the inequality for y:
3y/2 <= 39/2
y <= 13
So John's age is less than or equal to 13