to find a percentage of something we were taught this method 
%% x
—— • —— 
100 total price
you then want to multiply the total price by the percentage and then divide by 100 
so in this case 
20 x
—— • ——
100 $43.50
20•43.50=870
870/100= 8.7
so i believe 9,10,11 would all be correct. 
hope this helps!