Compare the time taken by the rc car to cover the same distance. do some go faster or slower?

There isn;t enough given values to define and determine what is asked. But since
distance = speed / time, time = distance / speed

Calculate the acceleration of a boat that has been cruising at 15 m/s but speeds up to 45 m/s in about 6 seconds. Don’t forget your units, m/s2. In order to calculate the acceleration of the boat we first have to identify the suited formula for acceleration in this scenario. 

Hence, a = vf – vi / t. Vi = 15 m/s Vf = 45 m/s T = 6 seconds   

Solution: 
A = 45 m/s – 15m/s / 6s 
A = 5m/s^2