Patrick B. answered 01/30/19
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Q = D+9
25Q + 10D = 645 <---- amount in pennies
25(D+9) + 10D = 645
25D + 225 + 10D = 645
35D + 225 = 645
35D = 420
D=420/35 = 12
12 dimes and 21 quarters ---> $1.20 + 5.25 = 6.45