8. The y-intercept is -10. You can find this by just seeing where the line would hit the y-axis. This is basically the starting point so the Scuba Diver's decent started at -10m.
9. You have the y-intercept so put that in slope-intercept form. y=mx+b
y=mx - 10
Now find the slope by picking two points and using the slope formula. I'll use
(30,-6) and (50,-4), and then plug in the values. 30 = x1, -6 = x2, 50 = x2, -4 = -4. Simplify.
m= y2-y1 -4 - (-6) 2 1
-------- = ----------- = --- / 2 = ---
x2-x1 50 - 30 20 10