A manometer is made of a tube of uniform bore of 0.5 cm2 cross-sectional areas, with one limb vertical and the other limb inclined at 30° to the horizontal. Both of its limbs are open to atmosphere and, initially, it is partly filled with a manometer liquid of specific gravity 1.25. If then an additional volume of 7.5 cm3 of water is poured in the inclined tube, what is the rise of the meniscus in the vertical tube?
a. 4 cm b. 75 cm
c. 12 cm d. 15 cm