(y-2)4 + 21 You subtract two because the 21 accounts for it and then whatever you have left multiplied by 4 and added to 21 is the amount of years after conversion.
C=4x+3y Constraints: x is greater than or equal to 0 2x + 3y is greater than or equal to 6 3x - 2y is less than or equal to 9 x + 5y is less than or equal to 20