You have to write the proportion between the number of cups of sugar and the brownies you need those cups for:
[tex]1\dfrac{1}{2}\div 24 = x\div 36[/tex]
Getting rid of mixed fraction, we have
[tex]\dfrac{3}{2}\div 24 = x\div 36[/tex]
Solving for x:
[tex]24x=36\cdot\dfrac{3}{2}\iff 24x=54 \iff x=\dfrac{54}{24}=\dfrac{9}{4}=2\dfrac{1}{4}[/tex]
