#### Answer

a) The function for whales' depth with respect to time is d(s)=-3.5 -1.8s
b) After 4 minutes, the whales' depth is 435.5 m

#### Work Step by Step

a) The function was created by using the initial height of the whale which 3.5 meters below surface of water so it is negative. The slope is -1.8 because he Is going down at 1.8 m/s. The depth which is in meters, is a function of time which is in seconds because the rate of the driver going down is in m/s.
b) Depth at 4 min
s= 4 mins $\times$ $\frac{60 secs}{1 minutes}$ = 240 secs
d(240)= -3.5 -1.8(240) = -3,5 -432 = -435.5 m
Therefore the depth is 435.5 m.