A car is going 56km/h, it is accelerating at a rate of . How long would it take for it to obtain a speed of 90km/h?

For some reason i have some sort of brain block when it comes to conversion factors. Here is my attempt at an answer.

56km/h X X =15.56m/s

90km/h X X = 25m/s

25m/s-15.56m/s= 9.44m/s

=1.57s

answer=1.57s?