The general equation which describes this motion is:

s(t) = -(1/2)at^2+v_0(t)+s_0

Where,

s(t) is distance traveled from starting point.

"a" is the acceleration.

v_0 is initial velocity.

s_0 is initial starting distance traveled (which is zero here).

Thus,

s(t) = - (1/2)*11*t^2+50*t

s(t) = -11*t^2+50t

Use this to solve all your problems.