Abus traveling at 6 m/s accelerates for 15 seconds until it travels at 36 m/s. what was the bus's acceleration.

Acceleration = (change in speed) / (time for the change)   <== Memorize this

Change in speed = (speed at the end) minus (speed at the beginning)

Change in speed = (36 m/s) minus (6 m/s)  =  30 m/s

Acceleration = (30 m/s) / (15 s)

Acceleration = 2 m/s²