Thickness measurements of prehistoric Native American pot shards discovered in a Hopi village are approximately normally distributed,

Question:

Thickness measurements of prehistoric Native American pot shards discovered in a Hopi village are approximately normally distributed, with a mean of 5.1 millimeters (mm) and a standard deviation of 0.9 mm. For a randomly found shard, what is the probability that the thickness is:
(a) Less than 3.0 mm?
(b) More than 7.0 mm?
(c) Between 3.0 mm and 7.0 mm?