For b. They are all correct, you can justify because all pairs are different versions of the same angle
When dealing with fractions, take the whole as 1.
in this case, the whole class is 1;
fraction of votes for Andrew: 1-1/2 -1/4 - 1/5
these fractions have different denominators (bottom), to continue, you have to make the denominators the same;
to do that, I usually count by the largest one. In this case, it is a 5. 5 is not divisible by 2 or 4, so I move on to 10. 10 is still not divisible by 2 and 4, so try 15, then 20.
20 works, so make all the denominators to 20. Remember 1 is 20/20:
20/20- 10/20 -5/20 -4/20 =1/20
so the fraction of votes Andrew got was 1/20.
For answer b, the whole is no longer 1. the whole is now 100.
1/2 of 100=50 for Amy
1/4 of 100=25 for Sophie
1/5 of 100=20 for Ryan
1/20 of 100=5 for Andrew
Notice the numbers add up to be exactly 100
Interpretation: For every $100 additional spent on advertising, the monthly sales revenue drops by $48.30. Personally I'd expect that the sales revenue increases with every $100 spent on ads.