The inside diameter of a randomly selected piston ring is a

The inside diameter of a randomly selected piston ring is a random variable with mean value 12 cm and standard deviation .04 cm.Suppose the distribution of diameter is normal.
a. Calculate P(11.99 <=X<= 12.01) when n 16.
b. How likely is it that the sample mean diameter exceeds 12.01 when n 25?