You may have chosen this answer because there are five more nickels than quarters and the number of coins is 30. However, to be correct the values need to make each of the conditions true. The correct system to start with is:

$\displaystyle{n}+{d}+{q}={30}\usepackage{cmbright}\Huge\$

$\displaystyle{0.05}{n}+{0.10}{d}+{0.25}{q}={3.45}\usepackage{cmbright}\Huge\$

$\displaystyle{n}={q}+{5}\usepackage{cmbright}\Huge\$ or $\displaystyle{n}-{q}={5}\usepackage{cmbright}\Huge\$