Answer:
150
Step-by-step explanation:
When y is directly proportional to x, y=kx and k=.
With the corresponding values we already know (3, 15), we can work out k.
k=, which is k= or k=5 when using those values.
Now that we know k, we can use it in the equation y=kx to get y.
We can substitute x for 30, as that's what we are working out, and k for 5 (as worked out above) to get y=30×5, which can be solved to y=150.
**This content involves rates of change/direct and inverse proportions, which you may wish to revise. I'm always happy to help!