Three capacitors A, B, and C are connected in a circuit as shown in figure. What is the charge in $\mu C$ on the capacitor B? 

Capacitors B and C are in parallel, then A is in series.

$C_{eq}=\frac{2\times (3+4)}{2+(3+4)}=\frac{14}{9}\mu F$

$Q=C_{eq}V=\frac{14}{9}(7-6)=\frac{14}{9}\mu C$

Q will be divided between B and C. So charge on B is

$q=\frac{3\times (14/9)}{3+4}=\frac{2}{3}\mu C$