Answer:
12
Explanation:
12 dimes is $1.20, so your total for the quarters is $3.25. Since there are 25 coins total and 12 of them are dimes, 25 - 12 = 13, so you have 13 quarters. 13 times its value of 25 cents leaves you with $3.25, fulfilling your needed total.
There likely was an easier way to do this, but I'm unfamiliar with it so I ended up doing this.