Question

a car increases it's speed from 20km/h to 50km/h in 10 seconds find its acceleration

Answer 1

acceleration = change in velocity / time
10/3600=1/360 h

Acceleration =50-20/1/360
=30×360
=10800 km/h^2

Answer 2

acc is
$\frac{chnge \: in \: velocity}{time \: taken} \: = \frac{(50 - 20) \times \frac{5}{18} \frac{m}{s} }{10 \: s}$
that is equal to
$0.83 \: \frac{m}{ {s}^{2} }$