If the base of the pool is 200 square feet in size, then we can just multiply 200 by the depth of 5 to equal 1,000 ft³ which is equal to the volume of the pool.
The answer is d (i.e. 51). the first 9 pages utilize 9 digits. the remaining 21 pages utilize two digits number. Therefore, 21*2=42 the total is 42+9=51
