That's a good question. I have both sliding miter saws and a table saw, so those details did not pose any questions for me.
If you have a sliding miter saw, you might be able to cut half of the 21-inch-long plank on one side, then flip it over and cut it on the other side. But I know not all miter saws are built the same and some have more capabilities than others. Still, I imagine there is a way if you get creative.
I "rip" slats less than 2 feet long all the time on my sliding miter saw that way using a standard 90-degree cut. Not the best method, but I currently have my table saw in winter storage in another garage. So, I make do. It works for me.

Another easier thought comes to mind. Do you have a small circular saw that you can dial in an angle cut? Even my oldest and least expensive Ryobi 18v circular saw can cut at an angle.
Here is good Google picture of a circular saw cutting off a board at an angle...
View attachment 3805004
You will not need a table saw if you have a circular saw to cut that 30-degree angle. All of my circular saws have that angle cutting feature, but to be honest, I don't think I've ever used that feature but maybe once or twice in my lifetime! I forgot about until thinking about your question!

If you don't have a circular saw, you might want to invest in one. I use my circular saws all the time. Even an inexpensive circular saw would be a good investment. I prefer my battery circular saws for portability, but a corded circular saw will cost less in most cases.
For example, Harbor Freight has this
7-1/4-inch electric circular saw currently on clearance...
View attachment 3805009
That particular saw has the ability to make a bevel cut from 0-45 degrees. You only need a 30-degree cut for this project.
At any rate, a circular saw is a lot less expensive than a table saw. It's also much easier to store a circular saw in a small space. Like I said, I have to put my table saw in winter storage in another garage because it takes up too much room in my main garage where I need to park my cars in the winter.