Answer :
Let us say that:
x = the time in seconds
y = depth of dolphin which is relative to the surface
The x intercept is located when y = 0, while the y intercept occurs when x = 0
We can see that at 0 seconds, the dolphin is still 42 feet below the surface:
x = 0, y = -42
The y intercept = -42 (0,-42)
After 14 seconds and at constant rate, the dolphin is now at the surface (0 below the surface):
x = 14, y = 0
The x intercept = 14 (14,0)
The slope is therefore m = (y2 - y1)/(x2 - x1) = 42/14 = 3.
Therefore, the formula for this line, in slope intercept form is
y = 3x - 42