9(3x+8y)

You take what's just left of the parentheses, which is 9,
and multiply it by the first term inside the parentheses, 3x.

When you do that you multiply the 9 by the 3, getting 27. Then
you write the x beside that.  You get 27x.

Then you take what's just left of the parentheses again, which is 9,
but this time you multiply it by the second term inside the parentheses,
which is +8y.

When you do that you multiply the 9 by the +8, getting +72. Then
you write the y besides that. You get +72y.

So you end up with

27x + 72y.

Edwin