Please help me with this proportion homework?

[Luke]

I really need help, completely stuck! Please help me, it'd mean a lot. Since it's a table, I can't just write out the questions, so here they are.
https://twitter.com/Fern1Dx/status/297435776390660096
https://twitter.com/Fern1Dx/status/297435973078376449
https://twitter.com/Fern1Dx/status/297435776390660096

[norcekri]

These all work the same way.
(1) Determine the ratio constant.
For instance, we're given "b is proportional to a^2". This means that the general form of the relation is
b = k a^2
We need to find k.
Use the table entry that has both b and a values.
80 = k 4^2
From which we get that k=5.

(2) When given a, compute b.
For instance, the next column gives us 15 for a, and wants a b value.
b = 5 * 15^2
This is simple math. I have no idea where someone got 240, but it's wrong.

(3) When given b, solve for a.
The third column gives us a b value of 405. Putting that into the equation, we get
405 = 5 a^2
81 = a^2
... from which getting the value of a is trivial.

See how it works?
Can you finish from here?