Question

The martinez family walked 3/5 of a mile in 3/8 of an hour. What equation can be used to calculate their unit rate in miles per hour?

Answer 1

mi/hr  that is the rate that you want so divide the miles by the time.

(3mi/5)/(3hr/8)

(3m/5)(8/3hr)

8mi/5hr

1.6 mph

Answer 2

$\bf \cfrac{\frac{3}{5}}{\frac{3}{8}}\cdot \cfrac{miles}{hour}\implies \cfrac{\underline{3}}{5}\cdot \cfrac{8}{\underline{3}}\cdot \cfrac{miles}{hour}\implies \cfrac{8}{5}\cfrac{miles}{hour}\implies 1.6\frac{miles}{hour}$

one may note that, you  never posted the equations list, but anyway, that'd be the rate in simplified form.