Let me help you with this :)
John = x
Mike = y
x = 4 + 3y (4 more than 3 times)
x + y = 20 (we put the x above into this equation)
4 + 3y + y = 20
4y = 16 (we transfers the 4 on the left side to the right side and subtract it from the 20)
y = 4 (the answer is 4)
we use this for the equation:
x = 4 +3*4
x = 16
John is 16 years old and Mike is 4 years old :)
