One situation would be :
Let's say The price of a pen, lets take it as y, is 4 times that of an eraser.
And let's say the price of an eraser is x.
Therefore
[tex]y = 4x[/tex]
Or of you prefer:
Let's say the length of one side of a square field is x.
And the perimeter of a square field is y.
perimeter of a square = 4 times the length of one side.
Thus,
[tex]y = 4x[/tex]
