$3\mathrm{.}77$ Determine $($a$)$ the difference in pressure and $($b$)$ the differ$-$

ence in piezometric head between points A and $B.$ The elevations

$z_A$ and $z_B$ are $10$ m and $11$ m $,$ respectively, $l_1=1m,$ and the

manometer deflection $l_2$ is $50$ cm $.$