We need to find pressure when h = 85 ft
We know the formula for pressure P = hρg, where h is the height of liquid, ρ is the density of liquid and g is the acceleration due to gravity value.
We have ρ = (0.001h+1.60)slug/
= 515.24 kg/
h = 25.908 m
g = 9.8m/

So pressure, P = 25.908*515.24*9.8 = 13088.61 N/

= 18.97 psi