Answer
$0.16cm$
Work Step by Step
We know that
$P_{at}+\rho_w gh_3+\rho_{oil}gh_1=P_{at}+\rho_{oil}gh_2$
This simplifies to:
$h_3=\frac{\rho_{oil}(h_2-h_1)}{\rho_w}$
We plug in the known values to obtain:
$h_3=\frac{(920)(0.0500-0.0300)}{1000}$
$h_3=0.0184m$
Now $h_4=h_2-(h_1+h_3)$
We plug in the known values to obtain:
$h_4=0.0500-(0.300+0.0184)$
$h_4=0.0016m=0.16cm$
