Fill in the blanks: when solving an equation, you must first the variable.

Monthly water bills for a city have a mean of $108.43 and a standard deviation of $32.09. find the probability that a randomly selected bill will have an amount greater than $155, which the city believes might indicate that someone is wasting water. would a bill that size be considered unusual?

Collin did the work to see if 10 is a solution to the equation r/4=2.4

Will give a: 122 b: 90 c: 48 d: 180