To find how many miles the whale swims in 16 days, we first need to determine its average speed. The whale swims 200 miles in 5 days, so its average speed is:
\[ \text{Average speed} = \frac{200 \text{ miles}}{5 \text{ days}} = 40 \text{ miles per day} \]
Now, to find out how many miles it swims in 16 days, we can use the equation:
\[ \text{Distance} = \text{Speed} \times \text{Time} \]
Thus, the equation for the distance (y) the whale swims in 16 days (16) is:
\[ y = 40 \times 16 \]
This matches option B.
So, the correct response is B. y = 40 x 16.