Correct. Use the joint variation equation $\displaystyle{y}={k}{x}{z}\usepackage{cmbright}\Huge\$ to find k.

$\displaystyle{160}={k}{\left({4},{000}\right)}{\left({2}\right)}\usepackage{cmbright}\Huge\$

$\displaystyle{0.02}={k}\usepackage{cmbright}\Huge\$

Use this value for k to find the interest earned on $5,000 for 3 years:

$\displaystyle{I}={0.02}{\left({5},{000}\right)}{\left({3}\right)}\usepackage{cmbright}\Huge\$

$\displaystyle{I}={300}\usepackage{cmbright}\Huge\$