You may have divided the numerator by 12 and got 7 instead of 6. Although $\displaystyle\frac{{7}}{{10}}\usepackage{cmbright}\Huge\$ is in lowest terms, it is not equivalent to $\displaystyle\frac{{72}}{{120}}\usepackage{cmbright}\Huge\$ . The correct answer is: $\displaystyle\frac{{3}}{{5}}\usepackage{cmbright}\Huge\$