So you have initial velocity, final velocity, and time. One easy equation for this (that will give you acceleration) is V=vo+at
When plugged in this would become
59km/h=51km/h+a(2 hrs)
To graph the equation, if graphing for velocity, Make the x axis time, using scaling as either every half hour or every hour. And obviously y axis velocity. Once you have that you can graph your initial velocity and final velocity. If your teacher doesn’t want a super exact graph, Then you can eyeball it and use a curve but you need to find out the acceleration in order to do that because the car is accelerating meaning that the graph line will not be linear, rather it will be exponential.