Answer:
[tex]7.5\ seconds[/tex]
Step-by-step explanation:
The Equation of motion is given by
[tex]v=u-at\\\\\ v:Final\ Velocity\\u:Initial\ Velocity\\a:acceleration\\t:time[/tex]
Here[tex]v=0(as\ at\ the\ end\ car\ stops), u=30m/s,a=-4m/s^2[/tex]
[tex]0=30-4t\\\\4t=30\\\\t=\frac{30}{4}\\\\t=7.5\ seconds[/tex]