Question 770139
<pre>
The formula is

h = h<sub>o</sub> - 16t²

h = the variable height the ball is above the river at variable time t.

h<sub>o</sub> = the height above the river that the ball is dropped = 150 ft.

When the ball hits the surface of the water is is 0 ft above the river.

So we set h = 0 and h<sub>o</sub> = 150 and solve for t

0 = 150 - 16t²

16t² = 150

  t² = {{{150/16}}}

Take the square root of both sides, (we don't need ± because
time is never negative.

   t = {{{sqrt(150/16)}}}

   t = {{{sqrt(150)/4}}}

   t = {{{sqrt(25*6)/4}}}
  
   t = {{{5sqrt(6)/4}}} or 3.06 seconds approximately.

Edwin</pre>