Answer:
9 nickels
Explanation:
Set the number of pennies as x. The number of nickels would be 31 - x.
The pennies are worth x cents and the nickels are worth 5 * (31 - x), or 155-5x.
We are given that he has 67 cents, so:
x + 155 - 5x = 67
Solve.
-4x = 67 - 155 = -88
x = 22
Nickels are 31 - x, so the number of nickels he has is 9.
I hope this helps!