Let the length of oil column `=CD=xcm`
Length of glycerine `=AB=10 cm`
`:. DE=(10-x)cm`
Equating pressure at horizontal level `BE` in both arms, we have
`P_("oil")+P_(Hg)=P_("glycerine")`
`xd_("oil")g+(10-x)rho_(Hg)g=10d_("glycerine")g`
or `x(0.8)=(10-x)13.6=10(1.3)impliesx=(136-13)/12.8=9.6cm`