It appears that you simply subtracted the numerators and subtracted the denominators and then simplified. You must first find the least common denominator, which in this case is $\displaystyle{y}{\left({y}+{4}\right)}{\left({y}+{3}\right)}\usepackage{cmbright}\Huge\$ , and then rewrite each fraction as an equivalent fraction using this denominator. Then subtract the numerators while keeping the denominator the same.