stone falls rest top cliff second stone thrown downward same height 34

A stone falls from rest from the top of a cliff. A second stone is thrown downward from the same height 3.4 s later with an initial speed of 66.64 m/s. They hit the ground at the same time. How long does it take the first stone to hit the ground? The acceleration of gravity is 9.8 m/s2 . Answer in units of s