Step-by-step explanation:
Let denote a normal random variable with mean and standard deviation . (That is: .) By definition, the -score of an observation with value would be:
In this question, the value of is given. Also given are the value of the observation and the corresponding -score, . Rearrange the -score definition to find an expression for :
Substitute in the value of , , and to find the value of , the mean of this normal random variable: