Can someone explain this maths questions and how you work it out?

Sure. So these are all fractions of course, and in order to add them up it's easiest if the bottom number is the same for each one. To do that, you find a number that they all multiply up to easily. In this case, 12. To get the 3 in 2/3 to twelve you have to multiply it by 4, so you do that to the top number too.

To get the 4 in 1/4 to 12, you have to multiply it by three, so you do that to the top number as well. The end result of bringing all three bottom numbers up to twelve and multiplying their top numbers as you do it is 8/12 + 3/12 + 6/12.

From there you just add up the top numbers. 8+3+6=17, so the final answer is 17/12.

I didn't take a lot of math in English so I'm not sure about the terms here.

You need a common denominator to add them. So you need to make the lower number the same for each one by multiplying them accordingly.
4)2/3 = 8/12.
3)1/4 = 3/12.
2)3/6 = 6/12.
And then you can just add all the top parts together.
8/12 + 3/12 + 6/12 = 17/12 = 1 5/12.

2/3 = 8/12
1/4 = 3/12
3/6 = 6/12

Go to the common denominator.For 2/3 plus 1/4 is the same as 8/12 plus 3/12 to give 11/12.Then 3/6 is the same as 612.Add the previous 11/12 to give 17/12.