A mercury manometer $\left(\rho=13,600 \mathrm{kg} / \mathrm{m}^{3}\right)$ is connected to an air duct to measure the pressure inside. The difference in the manometer levels is $15 \mathrm{mm},$ and the atmospheric pressure is 100 kPa. $(a)$ Judging from Fig. $\mathrm{P} 1-67,$ determine if the pressure in the duct is above or below the atmospheric pressure. ( $b$ ) Determine the absolute pressure in the duct.