a ball is dopped and falls with an accelerationof 9.8 m/s downward it hits the ground with a velocity of 49 m/s downward how long did it take the ball to fall to the ground

In order to know how long it has been falling for you take the final velocity "49m/s" and divide it by the acceleration "9.8m/s" and get 5, since you have been using seconds in the calculations the answer is 5 seconds. (Fun fact, it is actually 9.82m/s per second since it accelerates and they rounded it down.)