My answer is 7sSquare/3, was wondering do i need to factorise 7sSquare or maybe my answer is wrong
$\displaystyle \dfrac{24rs}{9t} \div \dfrac{8r}{7st}$
To divide fractions, flip n multiply: $\displaystyle \dfrac{24rs}{9t} \times \dfrac{7st}{8r}$
You can then cancel anything which appears on the top and bottom. For checking I get an answer of $\displaystyle \dfrac{21s^2}{9}$
edit: which cancels to $\displaystyle \dfrac{7s^2}{3}$ so your answer is fine (and doesn't need factorising)