I need help with this question!!

Ashopper bought a watermelon a pack of napkins and some paper plates in his state there was no tax on food the tax rate on non-food items is 5% the total for the three items he bought was 825 before tags and he paid $0.19 in taxes how much did the watermelon cost

The difference of 2 numbers is 21 and the quotient of the equation is 4 then what are the two numbers?

Me. i can't figure out this question. give an explanation too. .