Since this is a proportion, we cross multiply. 12/2=9/x (The variable "x" is used the represent the unknown number, and this is the number we are solving for) 12*x=2*9 (Cross multiply) 12x=18 (Simplify) x=18/12 (Divide each side by 12) x = 3/2 (Simplify fraction) The unknown number is 3/2, or 1.5.