Following the formula above if you want to get degrees Celsius you have to subtract 32 from degrees Fahrenheit multiply the result by 5 and divide it by 9.
So in case with 7 we have: ((7 - 32) × 5) ÷ 9 = (-25 × 5) ÷ 9 = -125 ÷ 9 = -13.888888888889 °C