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 4 we have: ((4 - 32) × 5) ÷ 9 = (-28 × 5) ÷ 9 = -140 ÷ 9 = -15.555555555556 °C