The depth of a scuba diver can be modeled by the equation d 0.5t (3.5t- 28.25), where d is the depth in meters of the diver and t is the time in minutes. find the time it takes for the diver to reach the surface. give your answer to the nearest minute.

We know that

using a graph tool
see the attached figure

The diver reaches the surface when d = 0
so
0.5t (3.5t- 28.25)=0---------> the solution is
0.5t=0--------> t=0
and
(3.5t- 28.25)=0----------> 3.5t=28.25--------> t=28.25/3.5--------> t=8.07 minutes


the time it takes for the diver to reach the surface is when the depth is zero
the time is 8 minutes

the answer is 
8 minutes