if y=6 when x=9 find x when y=12

Question

direct variation

Answer 1

 

y/x = constant

 

6/9 = 12/x ⇒

 

x = 12(9/6) = 18

 

Test the answer.

Answer 2

If this is direct variation, y = kx and so (9,6) tells you that k = 2/3.

 

Now you can substitute y=12 and this k value, and solve for the unknown x.