    
−       
= 
 − −   
2. The depth of a river at a certain point is modeled by the function W defined above, where
W t( )
is measured in feet
and time t is measured in hours.
(a) Find
W ' 8( )
. Using correct units, explain the meaning of
W ' 8( )
in the context of the problem
(b) The graph of
W
is concave down for
3 3.5  t
. Use the line tangent to the graph of
W
at
t = 3
to show that
W (3.5 9 )  .
(c) Find
( )
3
2
1
4
lim
t 2
W t t
→ t
− +
−
.