[tex]\frac{4s+3st}{s ^{2}t ^{2} } - \frac{s-2st}{s ^{2}t ^{2} } \\\\s,\ t \neq 0\\\\ \frac{4s+3st}{s ^{2}t ^{2} } - \frac{s-2st}{s ^{2}t ^{2} }= \frac{4s+3st-(s-2st)}{s ^{2}t ^{2} } = \frac{4s+3st- s+2st }{s ^{2}t ^{2} } =\frac{3s+5st }{s ^{2}t ^{2} } =\\\\= \frac{s(3 +5 t ) }{s ^{2}t ^{2} } = \frac{ 3 +5 t }{s t ^{2} }[/tex]
