There should be a typo in the question: the correct formula would be

Let's compute
first. We have

If we intersect this set with X, we have

So, that would be the left hand side. For the right hand side, we have

And their union is again 
Answer: 27
Step-by-step explanation:
The given sequence : 13, 24, 35, ....
Here, first term : a= 13
Common difference: d=24-13 =11
The nth term of arithmetic sequence is given by :-

It is given that the nth term is 299, so put

Subtract 13 from both sides , we get

Divide both sides by 11, we get

Add 1 on both sides , we get

Hence, the value of n= 27
It depends how many decimal points you are moving. If it's 1 decimal point then the point would move to the right and the answer would be 3246.50if it was two decimal places then it moves two to the right and the answer would 32465.0. But you don't need to put the .0 at the end so it will be 32465