The liquid in the open-tube manometer in fig. 12.8a is mercury, y1 = 3.00 cm, and y2 = 7.00 cm. atmospheric pressure is 980 millibars. (a) what is the absolute pressure at the bottom of the u-shaped tube? (b) what is the absolute pressure in the open tube at a depth of 4.00 cm below the free surface? (c) what is the absolute pressure of the gas in the container? (d) what is the gauge pressure of the gas in pascals?