The manometer shown below is used to measure the difference in water level between the two tanks. Calculate this difference for the conditions indicated.

Explanation

`P_(a) + h_(1) rhog - 40rho_(1)g + 40rhog = P_(a) + h_(2) rhog`
`h_(2) rhog - h_(1) rhog = 40 rhog - 40 rho_(1)g`

as `rho_(1) = 0.9rho`
`(h_(2) - h_(1))rhog = 40rhog - 36rhog`
`h_(2) - h_(1) = 4 cm`