f×12
17 - f×12
[To find how much something exceeds you subtract] 17 - f×12 -
17 - f×12 - ×17
17 - f×12 - ×17 = 6 17 - 12f - = 6 Multiply through by 3 to avoid fractions: 51 - 36f - 17 = 18 34 - 36f = 18 -36f = -16 f = f = Edwin