If y = 6 when x = 10, find x when y = 18.
Use a proportion
Let y be the numerator and x the denominator
You will find that 6x=180
Or set up a ratio.
you know that y:x :: 6:10
you are looking or 18:?
because 6*3=18, you can multiple the y by 3 to get the x which is 30.