Thirty boys and x girls sat for a test. The mean of the boys' and girls' scores were 6 and 8 respectively. Find x if the total score was 468.

The mean of the boys' scores is $6$ and there are $30$ boys. This means that the sum of the boys scores is $6 × 30 = 180$. The mean of the girls' scores is $8$ and there are $x$ girls so the total of all the girls' scores will therefore be $8 × x = 8x$. Because the total score is $468$, $180 + 8x = 468$ and $x = 36$.