Let's x=number of pannies, and y=number of nickels
x+y=27
2.5x+5y=117.5
Now you need to solve this system of two equations.
x=27-y
2.5(27-y)+5y=117.5
67.5-2.5y+5y=117.5
2.5y=50
y=20
x=27-20=7
total: 1 dollar and 7 cents.
7 pennies =7 cents
20 nickels= 1 dollar