The answer should be $2\mathrm{.}32$x$109$ lbf $.$ How do I get this answer?

The figure shows a cross section of a submerged tunnel under two immiscible liquids. The top liquid has a specific gravity of $S{G}_1=0\mathrm{.}5$ and thickness $h_1=15ft.$ The bottom liquid has a specific weight of $S{G}_2=1\mathrm{.}5$ and thickness $h_2=40ft$ The tunnel has a radius of $20$ ft and is $4$ miles long. Find the magnitude and location of the resultant hydrostatic force on the circular roof of the tunnel.