In the given figure the total charge stored in the combination of...

All the capacitors are in parallel combination and therefore potential drop across each capacitor would be the same.

Charge on the capacitor can be written as, $Q = CV$.

The charge on ${C}_{1}$ is ${Q}_{1} = 2 \times 10 = 20\mu C$

The charge on ${C}_{2}$ is ${Q}_{2} = x \times 10 = 10x\mu C$

The charge on ${C}_{3}$ is ${Q}_{3} = 3 \times 10 = 30\mu C$

By the given data.

${C}_{1} + {C}_{2} + {C}_{3} = 100\mu C$

$⇒ 10\left(2 + x + 3\right) = 100$

$⇒ x = 5$