The formula that converts degrees fahrenheit to degrees celsius is: c = 5/9 (f – 32) rewrite the formula to make f the subject.

A quick way to get an answer on a test is to double C and add 30. It gives a very close answer to the actual one. 

Multiply both sides by 9/5
9/5 * C = 9/5 * 5/9 (F - 32) Look what happens on the right side of the equation.The fractions become 1*1 / (1*1) which is just 1. The answer to that cancellation is 1/1 = 1

9/5 C = F - 32 Add 32 to both sides.
9/5 C + 32 = F <<<<<< answer.