Answer:
40 psi
Explanation:
We can see that the relationship is linear with pressure increasing by 5 psi for every extra 15 feet depth
The data is given from depth of 40 feet
At 40 feet, pressure = 10 psi
At 55 feet, pressure = 15 psi
At 70 feet pressure = 20 psi
We have to use 40 as the base depth since there are no measurements less than that value. So relative depth is d - 40 and since for every 15', there is an increase of 5psi, the relative increase in pressure per 15' is
But the base pressure is 10psi not 0 so we have to add 10 to this equation to get the absolute psi
So the equation that connects depth (d) and pressure (p) is:
If we plot these values, we can see they fit a straight line with slope = 1/3 and y-intercept = -10/3
Hope that helps