A stone falls from rest from the top of a cliff. a second stone is

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