x + y = 3.36 --> the boys are splitting $3.36
x = 3y - .12 --> one boy received $.12 less than 3 times as much as the other
--> substitute the second equation for the x in the first equation
(3y - .12) + y = 3.36 --> combine like terms
4y - .12 = 3.36 --> add .12 to both sides of the equation
4y = 3.48 --> divide both sides by 4
y = .87
the other boy gets $0.87
substitute into x = 3y - 12
x = 3(.87) - .12
x = 2.61 - .12
x = 2.49
the first boy gets $2.49