Answer: C

Small Hint:

The pattern repeats every $3$ entries along each row and column

Big Hint:

Since $20=3\cdot6+2$, two letters get one extra appearance in each line

Video solution:

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Written solution:

Since $20 = 3 \cdot 6 + 2,$ the bottom $2$ letters in each column will occur one more time than the third letter.

This means that the third letter in each column will occur $6$ times, whereas the other $2$ will appear $7$ times.

Across the $20$ columns, $P$ is the letter that appears $6$ times in $7$ columns and appears $7$ times in the other $13$ columns. The same is true of $R.$

Thus $P$ and $R$ each appear $7\cdot6+13\cdot7=42+91=133$ times.

$Q$ will therefore appear $$\begin{align*} 20 \cdot 20 - 2 \cdot 133 &=400 - 266 \\ &= 134 \end{align*}$$ times.

Thus, C is the correct answer.