Calculate the Distance of lightning

[Crookedsky]

Hello all,
Determine a number N so that if the number of seconds (t) between flash and thunder is divided by N, the result is the distance (d) in miles. Be sure to specify the units of N. The speed of sound in air is 343 m/s. Assume the travel time of light is negligible. D = t/N

So would i convert 343 m/s to feet and then convert feet to miles? I am confused...

 

[SHISHKABOB]

think about it in terms of units

D is in miles, t is in seconds and N is in terms of...?

if you want miles = $\frac{seconds}{N}$, what should N be in units?