Question 1005780
Call the number of dimes and nickels, d and n.  Then we have
d + n = 77 and the value equation is
10d + 5n = 615  (we work in cents)
Now multiply the top equation by five and subtract from the second...
10d + 5n = 615
-(5d + 5n = 385)
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5d = 230
d = 46 dimes
n must be 31 nickels