We know that this ratio is directly because the two magnitudes go up.
In this case we will get the proportionality constant by dividing any term of the second magnitude by the first.
For example:
[tex]9 \: \div \: 3 \: = \: \boxed{3}[/tex]
Now that we know that k = 3, we can know how much "y" will be if x = 5.
We just multiply:
[tex]3 \: \times \: 5 \: = \: \boxed{ \bold{ 15}}[/tex]
Answer: y = 15
