Quantity of farmland owned by Pam = 7.5 square miles. The other important information given in the question is the equation relating square miles and acres. Using that information, the answer to the question can be easily reached. a = 640s = 640 * 7.5 acres = 4800 acres. From the above deduction, we can conclude that the correct option among all the options that are given in the question is the third option or option "C".
You can multiply by 12 because to get rid of the fractions all terms should be divided by the LCM (ie the smallest multiple that is exactly divisible by 2, 4 and 3)
Multiples of 3 = 3, 6, 9, 12
Multiples of 4 = 4, 8, 12, 16
Multiples of 2 = 2, 4, 6, 8, 10, 12
Therefore the fractions should be multiplied by 12