pressure at B = pressure at C

or, using psi units, p’_{A}+\frac{\gamma h}{144}(oil)=p’_{D}+\frac{\gamma h}{144}(mercury)

20.0+\frac{(0.750\times 62.4)(2.75+h)}{144}=\frac{(13.57\times 62.4)h}{144} and h=3.76 ft

Another method:

    Using convenient feet of water units,

pressure head at B = pressure head at C

\frac{20.0\times 144}{62.4}+(2.75+h)(0.750)=13.57h and h=3.76 ft, as before