[tex]\bf 20in\cdot \cfrac{2ft}{24in}\implies \cfrac{20\boxed{in}\cdot 2ft}{24\boxed{in}}\implies \cfrac{20\cdot 2ft}{24}[/tex]
the idea being, you use their equivalent in a fraction,
and you put the unit you want cancelled, at the top or
bottom of the fraction, depends on where you need it,
since for the sake of ratios a/b is the same as b/a,
so you really can flip the ratio equation to suit you
what unit you want to cancel
