keeping in mind that there are 5280 ft in 1 mile, and there are 60 minutes in 1 hr and 60 seconds in 1 minute, therefore 60*60 seconds in 1 hr, or 3600 seconds, then.
[tex]\bf \cfrac{40\underline{mi}}{\underline{hr}}\cdot \cfrac{5280ft}{\underline{mi}}\cdot \cfrac{\underline{hr}}{3600s}\implies \cfrac{40\cdot 5280}{3600}\cfrac{ft}{s}\implies \cfrac{176}{3}\implies 58.\overline{66}\frac{ft}{s}[/tex]
