Math Help - Variation

1. Variation

"A varies directly with B when C is constant and inversely with C when B is constant. A=6, B=2 and C=3. What is the value of A when B = 3 and C= 18?"

What I really don;t know here is how to form the equation/ statement. I've never really come acroos this question.

Thanks

2. Re: Variation

The statement "A varies directly with B when C is constant and inversely with C when B is constant" means:

$A=k\cdot\frac{B}{C}$

You may use the given information to find the constant of proportionality $k$.