The writing is confusing, but as I understand it 21 is about 20% of 104 (21x100/104). The same prosentage of 500 equals 100,96 and I would round it to 101 (the answer of the first equasion x 500/100).
Divide to undo the multiplication of n times 72. Move the decimal point two places to the right to write the decimal as a percent. You can estimate to see if the answer is reasonable. Use 10% and 20%, numbers close to 12.5%, to see if they get you close to the answer.
Hope this helps
Survive because your persevering through a tough time
35% of 70 is 24.5
Hope this helps!