Weighted Balls

You have a bin of weighted balls. It consists of red balls and black balls. The red balls weigh $n$ kilograms each, and the black balls weigh $m$ kilograms each. The probability of selecting a black ball uniformly at random is $\frac{1}{k}$. What is the minimum total weight of the balls in the bin? Solve when $k=8, m=10$ and $n=2$