Hi Mirsha,
The question says that p is a linear function of x.
The general formula of a linear function is--> p(x) = mx + b
Now let's substitute the pressure of 1 at zero depth--> 1 = 0m + b
b = 1
Now let's substitute the pressure of 3.92 at a depth of 100 feet--> 3.92 = 100m + 1
Subtract 1 from both sides-->2.92 = 100m
Divide both sides by 100--> m = .0292
So the linear function is--> p(x) = .0292x + 1
Dan