The equation $y = -4.9t^2 - 3.5t + 2.4$ relates the height $y$ (in meters) to the elapsed time $t$ (in seconds) for a ball thrown downward at 3.5 meters per second from a height of 2.4 meters from the ground. In how many seconds will the ball hit the ground? Express your answer as a decimal rounded to the nearest hundredth.
You can factor that equation to this: 49t^2+35-24=0
Now, factor this, and one of its roots will be positive. That positive root is the answer.
(or, if you can't factor this, Use the quadtradtic formula!)