How many bricks are used in paving the patio in this math question?

Question

The following math problem is from Mathematics Olympiad for primary school students. I calculated the number of bricks needed as 961 but the key doesn't give that number. Please help see whether I was wrong and if so, what is the right answer. Thank you.

Answer 1

Let's say bricks are rectangles $1\times 3$ or can be rotated to $3\times 1$, so that $3$ bricks form a square $3\times 3$.
So, if Alex wants that pattern as the displayed, she should take $m\times m$ of $3\times 3$ squares of bricks, which is $3m^2$ ones.
So the task is to find maximal integer $m$ for that $3m^2\le 999$ holds.
That is $$m^2\le \frac{999}{3}$$ $$m\le \sqrt{\frac{999}{3}}$$ where $\sqrt{.}$ is square root and $m$ maximal integer, so wiki: Floor and ceiling functions reads

In mathematics and computer science, the floor function is the function that takes as input a real number $x$ and gives as output the greatest integer less than or equal to $x$, denoted $\operatorname{floor}(x) = \lfloor x\rfloor$.

So $m=\left\lfloor\sqrt{\frac{999}{3}}\right\rfloor$ and the number of blocks is $3m^2=3\left\lfloor\sqrt{\frac{999}{3}}\right\rfloor^2=972$