You need to remember what is the formula of velocity in uniformly accelerated motion such that:
`v^2 final = v^2 initial + 2*a*d`
The problem provies the initial velocity v initial = 50 mi/h and the final velocity needs to be zero since the car comes to a stop such that:
`0 = 50^2 + 2a*d`
You need to convert the miles in feet since the velocity is given in miles per hour and decceleration is gven in feet/`s^2` .
`1 mi = 5280 feet =gt 50 (mi)/(hour) = 5280*50(feet)/(60 sec) = 4400 (feet)/(sec)` `0 = 4400^2 - 2*42*d =gt d = 4400^2/84`
`d = 230476.1 feet`
Hence, evaluating the distance covered before the car comes to a stop yields `d = 230476.1` feet.