Question 65295
D(t)= -t^2+10t 
If this is put in the form
{{{D(t) = at^2 + bt + c}}}, the the maximum is at ({{{-b/(2a)}}},{{{D}}})
b = +10
a = -1
-b/(2a) = -10/-2
-10/-2 = 5
D(5) = -(5)^2 + 10*5  
D(5) = -25 + 50
D(5) = 25
so, the maximum is at (5,25)
He fishes at a depth of 25 in 5 hours. Is D in units of feet?
Problem didn't say.