Acceleration = (change in speed) / (time for the change).
= (35 km/hr) / (30 sec)
= 7/6 km/hr-sec .
To get rid of that ugly unit, and change the solution to a
more familiar unit of acceleration, we need to convert it
to the usual ' m/s² '. This is not a major operation.
(7/6 km/hr-sec) x (1000 m/km) x (1 hr/3600 sec)
= (7/6 x 1,000 ÷ 3600) km-m-hr / km-hr-sec-sec
= 0.324 m/s² (rounded)
(This a rather gentle acceleration ... about 0.03 of a 'G' ...
so it would not mash you back into your seat in the car.)