Hey there!
First of all, let's find the area of the pool.
15(30)=450 feet squared.
Now, let's find the area of the triangle.
4(3)=12/2=6 feet squared
Assuming that you can land anywhere in the pool, including the diving board (as we didn't get any measurements for it so that we can eliminate it)
This gives us 6/450, which simplifies to 1/75.
Therefore, you have 1/75 or 1.3% chance of landing on the raft.
I hope this helps!