A bottlenose dolphin is 10 feet below sea level. Then it begins to dive at a rate of 9 feet per second. What is the equation of the line that represents its elevation, y, after x seconds?

A.

y = 9x - 10

B.

y = - 9x - 10

C.

y = 9x + 10

D.

y = - 9x + 10

Diving means it is moving down so it would be a negative value.

You would need to multiply the rate by the number of seconds it dives, so you would have - 9x for that part.

The dolphin started at 10 feet below sea level which would be written as - 10.

To find the elevation you would need to add both parts together, which would give you:

y = - 9x - 10

The answer is B.