Problem $2\mathrm{.}6\mathrm{.}27$

In Fig. P$2\mathrm{.}6\mathrm{.}27,$ pipe A contains gasoline $(SG=0\mathrm{.}7),$ pipe $B$ contains oil $(SG=0\mathrm{.}9),$ and the manometer fluid is mercury. Determine the new differential reading if the pressure in pipe $A$ is decreased $25$ kPa $,$ and the pressure in pipe $B$ remains constant. The initial differential reading is $0\mathrm{.}30$ m as shown.

Please help with solving as well as finding SG Mercurt.