A strain of long-stemmed roses has an approximate normal distribution with a mean stem length of 15

Question:

A strain of long-stemmed roses has an approximate normal with a mean stem length of 15 inches and standard deviation of 2.5 inches.
a. If one accepts as "long-stemmed roses" only those roses with a stem length greater than 12.5 inches, what percentage of such roses would be unacceptable?
b. What percentage of these roses would have a stem length between 12.5 and 20 inches?
Distribution
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