An oil with a density of $0\mathrm{.}91$ g$/$cm$\backslash$deg is flowing in a pipe at $60\backslash$deg F and the flowrate of this oil is measured with a mercury manometer. The density of mercury is $13\mathrm{.}546$ g$/$cm$\text{'}.$ If the difference in height of the two legs of the manometer is $0\mathrm{.}78$ in$.$

what is the pressure difference between points A and B in mmHg$?$