I need help with algebra 2 :)
I need to know how to make an equation with direct and in verse variations. A sample problem is:
Suppose that y varies directly with x and at the same time varies inversely with z, and y=12 when x=6 and z=-2.
a) y= -4x/z
b) y= 4x/z
c) y= -4z/x
d) y= 4z/x
I'm not looking for an answer but I really would love if someone could kinda walk me through the steps and help me learn how to do it because the way my teacher is explaining it really doesn't help me much. I'm very lost. :(

Question

I need help with algebra 2 :)
I need to know how to make an equation with direct and in verse variations. A sample problem is: 
Suppose that y varies directly with x and at the same time varies inversely with z, and y=12 when x=6 and z=-2. 
a) y= -4x/z 
b) y= 4x/z 
c) y= -4z/x 
d) y= 4z/x 
I'm not looking for an answer but I really would love if someone could kinda walk me through the steps and help me learn how to do it because the way my teacher is explaining it really doesn't help me much. I'm very lost. :(