OE

First you should write x as a decimal in order to calculate x^2. This gives x = 0.8 and x^2 = 0.64. The percent difference is equal to the actual difference divided by the basis of the comparison. The basis of the comparison is what follows the word “than” in the problem statement

percent difference 0.8-0.64/0.64=1/4=25 %

Note that if the problem had instead been worded as “by what percent is 0.64 smaller than 0.8?” the basis of the comparison would have been 0.8. The answer in that case would have been 20 %.

D is the answer