The Total Revenue R Earned Per Day (In Dollars)from a Pet-Sitting

Multiple Choice

The total revenue R earned per day (in dollars) from a pet-sitting service is given by? $R ( p ) = - 10 p ^ { 2 } + 120 p$ ? where p is the price charged per pet (in dollars) .
?
Find the price that will yield a maximum revenue.
?

A) $7.00
B) $10.00
C) $8.00
D) $6.00
E) $9.00