2014 AMC 12B Problem 1

Let $n$ be the number of nickels, so Leah has $13-n$ pennies. One more nickel would give her $n+1$ nickels, and this equals the number of pennies: $$n+1 = 13-n.$$ Solving gives $n=6,$ so there are $6$ nickels and $7$ pennies. The total value is $6\cdot5 + 7 = 37$ cents. Thus, the correct answer is C.