Let d represent the number of dimes. Then the value of the coins can be written as ...
0.10d +0.25(46 -d) = 9.25
-0.15d = 9.25 -(0.25*46) = -2.25 . . . . simplify, subtract .25*46
d = 2.25/.15 = 15 . . . . . . . . . . . . . . . . . divide by the coefficient of d
There are 15 dimes.