Discrete Probability Distributions

Ok I think this is a hypergeometric probabiltiy question but I can't break down the numbers.

Six Chevy vans are being tested by consumer Reports for quality control. In the past, 40% of the vans tested have had some safety problems on delivery such s headlight out or a seatbelt not working, If a sample of 6 vans is taken:

a) what is the probability of four of the vans having a safety problem?

b) what is the expected number of vans in the sample that will have a safety prolem?

I can them if I knew where to break it a part.

The formula I have is P(x)=aCx^x-aCr-x

But which numbers go where?

a=?

n=?

r=?

x=?