12x(8x-20)÷4(2x-5) please solve it

How do you answer this question? (step by step)

Can someone me i’m confused. will give brainliest and a whole bunch of points

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