The answer would be: D. y = 10x
The value of y is 30 when x is 3. Then, the ratio of y:x would be: 30/3=10
That means Y would be 10 times more than X. Then, the right choice would be: y = 10 x
You can check it by inserting the number(y=30. x=10) like this:
y = 10 x
30= 10(3)
30= 30