In the figure, if C1=C2=2C3= 28.7 uF, how much charge is stored on each capacitor when V=47.0 V?

your text does not match the text in the link. I'll assume the text is correct.

For C1, Q = CV = 28.7µ x 47 = 1349 µC
For C2 = 28.7µF and C3 = 28.7µF/2 = 14.35µF, you have two caps in series, and the value is
1/C = 1/28.7 + 1/14.35 = 0.0348 + 0.0697
C = 9.57µF
Total charge Q = CV = 9.57µF x 47 = 450µC
This same charge is on both C1 and C2

edit: next time, say so.

Q1 is charge on C1, etc. You should be able to figure that much out.