Potential difference across the branch de is 6V.
Net capacitance of de branch is 2.1μF
So, q=CV ⇒q=2.1×6μC ⇒q=12.6μC
Potential across 3μF capacitance is V=312.6=4.2Volt
Potential across 2 and 5 combination in parallel is 6−4.2=1.8V
So, q′=(1.8)(5)=9μC