Simon is 13.
Simon's age can be represented algebraically as x, thus the following equation can be drawn; 5(x-4) = 3(x+2).
Expanding the equation 5x-20 = 3x + 6, and moving the x's to one side, and the integers to the other you get 2x = 26, and x=13. To check results (13-4)*5=45, and (13+2)*3=45.
