Sue has $2.20 in dimes and nickels. If she has 13 more dimes than nickels, how many of each coin does she have?

10d+5n=220

divide both sides by 5

2d+n=44

d=13+n

sub 13+n for d in other equatin

2 (13+n) + n=44

26+2n+n=44

26+3n=44

minus 26 both sides

3n=18

divide both sides by 3

n=6

sub back

d=13+n

d=13+6

d=19

19 dimes

6 nickles