Paul eats 1½ dozen cookies in the first hour. If he continues eating cookies at the same rate, how many cookies will he eat in 3 hours?(Not in dozens)

1-1/2 dozen cookies = 12+6 = 18 cookies in 1 hour.

18 cookies/hour x 3 hours = ? cookies. Note that the unit hour cancels since one hour is in the denominator and the other hour is in the numerator. With no hour units left the only unit left is cookies and that's what you want in the answer. So you know the answer and procedure is plausible.