How to Start This Statistics Problem?

Since X is normal, (X-mu)/sigma is normal with mean 0 and variance 1. So P(X<=8)=P([x-6]/4<=[8-6]/4)=P(Z<=1/2) where Z is the standard normal distribution. You can then look this value up on a standard normal table or use a calculator. The same method can be used to solve the next two parts. P(7<=X<=10)=P(1/4<=Z<=1)=P(Z<=1)-P(Z<=1/… for part b and P(X>=11)=1-P(Z<=5/4).