Aparticle's acceleration is described by the function ax =(10 −t)m/s2, where t is in s. its initial conditions are x0 =0m and v0x =0m/s at t =0s.

Missing question: "At what time is the velocity again zero?"

Solution:

the acceleration of the particle is

the velocity of the particle is the derivative of the acceleration:

where  is the initial velocity, given by the problem.

So, to find when the particle's velocity is again zero, we should just put vx=0 and find t:

which has two solutions:
t=0 (beginning of motion)

and so, the particle velocity returns to zero after 20 seconds.

Then the answer would be d then