Hello there, you just need to enter how many elements are present in the union (AUB). You don't need to list out all. That's the catch :) Hope this helps!

they have just asked to specify the number of elements in aUb.....which is 8......aUb means all elements in a and b without repetetion.

How can I recommend this to folks who want to learn SQL if the mathmatical operators aren't defined before questions are asked about them. It's pretty hard to google set union if you've never seen it before... I'd love some more explanation for the math.

just ype answer. 8 and submit directyelly, don't click run the code.

If you are as confused as I was about submitting the answer this is how you do it: just type the number in the large text box and then click on the check against the custom input and put the same answer in the* smaller text box*. Then run the code and if it's okay just click the submit button :)