Combined capacitance in series = 1CT\frac{1}{C_T}CT1 = 1C1\frac{1}{C_1}C11 + 1C2\frac{1}{C_2}C21
The two capacitors have capacitance of 0.0003μF and 0.0006μF respectively
1CT\frac{1}{C_T}CT1 = 10.0003\frac{1}{0.0003}0.00031 + 10.0006\frac{1}{0.0006}0.00061 = 0.0002+0.00010.0006\frac{0.0002 + 0.0001}{0.0006}0.00060.0002+0.0001
1CT\frac{1}{C_T}CT1 = 0.00030.0006\frac{0.0003}{0.0006}0.00060.0003
CT{}_TT = 0.0002μF.