The result has the correct sign, but you multiplied the reciprocal of $\displaystyle-\frac{{7}}{{8}}\usepackage{cmbright}\Huge\$ , or $\displaystyle-\frac{{8}}{{7}}\usepackage{cmbright}\Huge\$ , by $\displaystyle-\frac{{3}}{{4}}\usepackage{cmbright}\Huge\$ . To divide, you need to multiply the first fraction by the reciprocal of the second fraction. The correct answer is $\displaystyle\frac{{7}}{{6}}\usepackage{cmbright}\Huge\$ .