Does anyone know the distance formula?

Solve each quadratic equation by factoring and using the zero product property. x^2 - 8x + 30 = 3x

The birth weights of newborn babies in the unites states follow in a normal distrubution with a mean of 3.4 kg and standard deviation of 0.6 kg. reaserches interested in studying how. children gain weights decide to take random samples of 100 newborn babies and calculate the sample mean birth weights for each sample

How do you find the distance of each number from the mean