Answer
$B)~134cm$
Work Step by Step
We can find the required focal length as
$f_{fluid}=[\frac{(n_{lens}-1)n_{fluid}}{n_{lens}-n_{fluid}}]f_{air}$
We plug in the known values to obtain:
$f_{fluid}=[\frac{(1.46-1)(1.50)}{1.46-1.50}](-7.75)=134cm$
