Question 1110637
Accelerating from rest at the rate of {{{55}}}{{{m}}}{{{"/"}}}{{{s^2}}} for {{{20 s}}} ,
the rocket would attain a speed of {{{55*20}}}{{{"m / s"="1100 m / s"}}} .
When it later decelerates with a constant {{{-35}}}{{{m}}}{{{"/"}}}{{{s^2}}} acceleration,
it takes {{{1100/35}}}{{{s}}} until it stops
During that slow down period the rocket's speed decreases linearly,
with an average speed of {{{1100/2}}}{{{"m / s"}}} .
During that period, travelling at that average velocity, it travels
{{{(1100/2)(1100/35)}}}{{{m=1100^2/70}}}{{{m=highlight(518571m)}}} (rounded to the nearest meter).
 
NOTE: I can write formulas, so if you want them ask,
but I saw no need to complicate a simple way to the solution.