h1+h2=20+20+5=45 ...............(I), since initially water was 20 cm in each arm.
Since pressure at bottom of both the limbs is equal after adding the immiscible liquid, we have
5×4×g+(h1−5)×1×g=h2×1×g
⇒h2−h1=15 ...............(II)
from (I) and (II), we have
h2=30,h1=15⇒h2h1=21