In order to find a solution to an algebraic equation such as this one we simply need to isolate the variable. We do this by applying the opposite operation to each side in order to get rid of the other factors and get the variable alone. Like so...
20 = y + 12 ... we need to subtract 12 from both sides to get rid of the 12 on the right side with the variable y.
20 - 12 = y + 12 - 12
8 = y
Finally, we can see that the value of the variable y is 8
You have to convert 50 feet to inches, so you take 50 times 12 and get 600. Then, you take 600/75 to get the number of rotations. Your final answer shold be 8 rotations.
