Twelve identical capacitors, each 8.0 µF and rated 50 V, are made into 3 strings in parallel…

Step 1. One string. Four equal capacitors in series give $\dfrac{8.0\ \mu\text{F}}{4} = 2.0\ \mu\text{F}$.

Step 2. The bank. Three strings in parallel add: $3 \times 2.0\ \mu\text{F} = 6.0\ \mu\text{F}$.

Step 3. The rating. In a string the voltage is shared equally, so each capacitor has a quarter of the string voltage. A capacitor reaches $50\ \text{V}$ when the string has $4 \times 50\ \text{V} = 200\ \text{V}$. The strings are in parallel, so the bank is limited to $200\ \text{V}$ as well.

Step 4. The charge. $Q = CV = 6.0\ \mu\text{F} \times 200\ \text{V} = 1200\ \mu\text{C}$.

What to learn. Strings in series raise the voltage rating. Strings in parallel raise the capacitance. It is the same idea as rows of cells.