Hope this helps ---------
let's firstly convert the mixed fraction to improper fraction, and then divide.
![\bf \stackrel{mixed}{11\frac{1}{2}}\implies \cfrac{11\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{23}{2}} \\\\[-0.35em] ~\dotfill\\\\ \cfrac{23}{2}\div \cfrac{3}{4}\implies \cfrac{23}{2}\cdot \cfrac{4}{3}\implies \cfrac{23}{3}\cdot \cfrac{4}{2}\implies \cfrac{23}{3}\cdot 2\implies \cfrac{46}{3}\implies 15\frac{1}{3}](https://tex.z-dn.net/?f=%5Cbf%20%5Cstackrel%7Bmixed%7D%7B11%5Cfrac%7B1%7D%7B2%7D%7D%5Cimplies%20%5Ccfrac%7B11%5Ccdot%202%2B1%7D%7B2%7D%5Cimplies%20%5Cstackrel%7Bimproper%7D%7B%5Ccfrac%7B23%7D%7B2%7D%7D%20%5C%5C%5C%5C%5B-0.35em%5D%20~%5Cdotfill%5C%5C%5C%5C%20%5Ccfrac%7B23%7D%7B2%7D%5Cdiv%20%5Ccfrac%7B3%7D%7B4%7D%5Cimplies%20%5Ccfrac%7B23%7D%7B2%7D%5Ccdot%20%5Ccfrac%7B4%7D%7B3%7D%5Cimplies%20%5Ccfrac%7B23%7D%7B3%7D%5Ccdot%20%5Ccfrac%7B4%7D%7B2%7D%5Cimplies%20%5Ccfrac%7B23%7D%7B3%7D%5Ccdot%202%5Cimplies%20%5Ccfrac%7B46%7D%7B3%7D%5Cimplies%2015%5Cfrac%7B1%7D%7B3%7D)
Y = -9x - 10
The dolphin is diving 9 feet per second so the rate of change is -9.
It's also 10 feet below sea level which makes the y-intercept -10
Hope this helped!