Urgent mechanics help please

"A train starts from rest and after 20s is travelling at 30m/s. It travels at this speed for 1 minute. Find the acceleration in the first 20s and the total distance travelled. What assumptions are inherent in the question?"

I found the acceleration in the first 20s to be 1.5m/s, and I think I found the total distance travelled to be 4800m but I searched it up and someone else said it's 1800m (their post didn't offer an explanation)

Please can someone let me know what the total distance travelled is, and how to get that answer, as well as what the assumption is because I haven't been taught that yet.

You should be able to work out the distance travelled in 1 minute at 30m/s (constant speed) and add it to the distance covered in the first 20s (constant acceleration, so suvat?)

The assumption is hinted at in the last sentance and you have covered it.

Oh wait is the assumption that the acceleration is constant? Thanks for the help

You used v=u+at to work out the acceleration and that assumes constant acceleration so yes.

Thank you so much!!!!!