9. (10 points) Given that 7 red balls and 5 white balls weigh 43 grams, and 5 red balls and 7 white balls weigh 47 grams, then 4 red balls and 8 white balls weigh $\qquad$ grams.
【Solution】Solution: $(47-43) \div(7-5)$ $=4 \div 2$ $=2$ (g)
$47+2=49$ (g)
Answer: 4 red balls and 8 white balls together weigh 49 g. Therefore, the answer is: 49.