180 coins total.
You need to find out how many pennies there are out of the 180 coins in Trey's piggy bank. So, you need to first find the total number of the other coins in the piggy bank. To do so, multiply each fraction by 180.
Dimes:
1/12 * 180 = 15 dimes
Quarters:
2/9 * 180 = 40 quarters
Nickels:
1/6 * 180 = 30 nickels
Now, you can add up the dimes, quarters, and nickels and subtract that from the total 180 coins to find out how many pennies Trey has in his piggy bank.
180-(15+40+30)=95
180-85=95