Which expression is equivalent to (5ab)^3/30a^-6 b^-7

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=

Can someone me and plz do the problem

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?