D, one number is positive and the other is negative. The only way it could equal 0 is to cross the other out. An example is, -5+5=0
Answer:I think a is:78.3 since it would be the same and since 0 doesn't have a value.
I think b is: 139.5 because all you are doing is subtracting 287.1-147.6
Total units would be: 4+7 = 11
value of 1 unit = 44/11 = 4
Ratio would be: 4(4) & 7(4) = 16 & 28