To find out if two fractions are equivalent or not, we multiply by a cross. That is, multiply the numerator of the first fraction with the denominator of the second fraction and multiply the denominator of the first fraction with the numerator of the second fraction and check that it gives us the same result. For example:
[tex]\begin{gathered} \frac{1}{3}\text{ and }\frac{2}{6} \\ 1\cdot6=3\cdot2 \\ 6=6 \end{gathered}[/tex]So, in this case, you have
[tex]\begin{gathered} \frac{3}{4}\text{ and }\frac{4}{3} \\ 3\cdot3\ne4\cdot4 \\ 9\ne16 \\ \text{ They are not equivalent fractions} \end{gathered}[/tex][tex]\begin{gathered} \frac{4}{5}\text{ and }\frac{8}{20} \\ 4\cdot20\ne5\cdot8 \\ 80\ne40 \\ \text{ They are not equivalent fractions} \end{gathered}[/tex][tex]\begin{gathered} \frac{8}{24}\text{ and }\frac{1}{3} \\ 8\cdot3=24\cdot1 \\ 24=24 \\ \text{They are equivalent fractions} \end{gathered}[/tex][tex]\begin{gathered} \frac{3}{12}\text{ and }\frac{1}{3} \\ 3\cdot3\ne12\cdot1 \\ 9\ne12 \\ \text{ They are not equivalent fractions} \end{gathered}[/tex]Therefore, the fraction pair that is equivalent is
[tex]\frac{8}{24}\text{ and }\frac{1}{3}[/tex]