in short simply we "multiply one fraction's top and bottom by the other's denominator", so let's do so,
[tex]\bf \cfrac{2\cdot 4}{3\cdot 4}\implies \boxed{\cfrac{8}{12}}\qquad \qquad \qquad \qquad \qquad \cfrac{3\cdot 3}{4\cdot 3}\implies \boxed{\cfrac{9}{12}}[/tex]
