It wont let me put the entire question here, so I put it in the description. Plz Help! I don't understand at all!

Question

A scuba diver dove from the surface of the ocean to an elevation of -79 9/10 feet at a rate of -18.8 feet per minute. After spending 12.75 minutes at that elevation, the diver ascended to an elevation of -28 9/10 feet. The total time for the dive so far was 19 1/8 minutes. What was the rate of change in the diver’s elevation during the ascent?

Answer 1

So you want to find the rate of change, so you want to find distance/time during the diver's assent. 

So first we need to find the distance covered by the diver.

-79 9/10 feet is -79.9 feet. -28 and 9/10 feet is -28.9 feet.

So to get the distance covered we need to subtract the diver's initial position from their final position.

-28.9 - -79.9 = 51 feet. So just looking at it, we can tell that looks right because the diver is ascending (going up), so the distance covered should be a positive number.

Next we need to find the time it took him to ascend. We know that the total time of his dive was 19 1/8 minutes, or 19.125 minutes. We know the diver spent 12.75 minutes at the bottom. We then need to find out how long it took him to dive to the bottom. To do that we divide the number of feet he dove by his rate of diving. 

-79.9 ft / (-18.8 ft/min) = 4.25 minutes

So we subtract the time he spend descending and the time spent on the bottom from total time. 

19.125 - 4.25 - 12.75 = 2.125 minutes

 

So he ascended 51 feet in 2.125 minutes, so we get 51 ft/ 2.125 min = 24 feet / minute as a final answer.