In Exercises 72 through 75, the velocity v(t) = x'(t) at time t of an object moving along the x axis is given, along with the initial position x(0) of the object. In each case, find:

(a) The position x(t) at time t.

(b) The position of the object at time t = 4.

(c) The time when the object is at x = 3.

x'(t) = −2(3t + 1)^1/2; x(0) = 4