Write a two-column proof to verify each conjecture. If -3r + 1/2=4, then r= -7/6. This is for geometry btw. Any help would be much appreciated, thanks.

Jane is cooking beans and rice for dinner tonight. she has 4 cans of black beans, 6 cans of red beans, and 3 cans of garbanzo beans in her cupboard. if she grabs a can of beans without looking at the label, what is the probability of her making black beans and rice for dinner?