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You cannot use the actual capacitance of X for the first part because you don't know the don't know the potential difference across X. So it is easier to use the effective capacitance and the total potential difference. Otherwise you can also do it by the longer method if you want to use the actual capacitance.
First calculate the potential difference cross X.
Total resistance in series is 12 micro farad and 24 micro farad from the parallel combination. So, potential across X=
(capacitance of X/ total capacitance in series) * 9
(1/12)/(1/12+1/24) * 9 = 6v
Now use Q =CV for X
Q = 12 micro farad * 6 =7.2* 10^-5 =72 micro C
You get the same answer, just a longer calculation.
For Y you can use the actual capacitance because you already know the potential difference cross Y from your previous calculations.
Sorry, but farad is resistance? I thought it was the capacitance. So you can use it to calculate p.d. just like actual resistance?