Answer:
Option C is correct.
Number of gallons of paint Ritchie needs to buy; 
Step-by-step explanation:
Unit rate defined as the rates are expressed as a quantity as 1 such as 8 miles per hour or 5 meter per second.
As per the statement: Ritchie wants to paint his bedroom ceiling and four walls. Both the ceiling and walls are 8 by 8 feet.
Area of four wall =
square feet
also;
Area of ceiling =
square feet
Total area of ceiling and four walls =
square feet. {Using distributive property
}
Also, it is given a gallon of paint cover 40 square feet.
⇒Unit rate per area =
gallon of paint
We have to find the number number of gallons of paint.

Substitute the given values we get;

Inverse of Multiplication operation is Division.
Therefore, number of gallons of paint Ritchie need to buy is, 