My god. So many people arguing demonstrably incorrect things.
It is 3+3+3+3+3 simply because the rules of repeated addition say that the first number is how many sets you have and the second number is how many are in each set.
How it reads to you is entirely irrelevant as you didn't define the rules!
Stuff like this is embarrassing.
Exactly that.
I was taught x meant times. So if have written 3 3 3 3 3 as it's 5 times 3.
That said, I don't like the way maths is taught now. Kids getting correct marks for part a question. Would love to see that in the real world. Sorry Mr taxman. I know I underdeclared significantly, but if you check my workings I got it all right except the initial 20% where I used 2% 😤