How do you find what number you need to get a certain average?

1.you add up all of the numbers you have
2.subtract the number you get from the average
3.if you know how many numbers there is then you know how many numbers you need to get
4.divide the number you got from the problem you made from step 1 & 2
5.what numbers you get from that are the numbers you needed to find

Let x and y be the number of quarters and half-dollars respectively.x+y=)0.25x+ 0.5y=)4×(): y=2020then x=2828-2020=808hence, he has 808 quarters.