Question

Variable y varies directly with variable x, and y = 6 when x = 9.

Answer 1

X and y are proportional hence when y is multiplied by a number, x is multiplied by the same number.

18=6*3 hence when y=18,x=9*3=27

x=27

Answer 2

So you can set up a proportion like
x/y=x/y
9/6=x/18
simplify 9/6=3/2
3/2=x/18
multiply both side by 18
(3x18)/2=x
54/2=x
x=27