Explain in detail how to add and regroup 28+5

This is simple. If you add 5 and 8 together, you get 13. What you do, is add the 1 to the 2, you get 3. The 3 in the 13 stays the same, so the awnser is 33.

Easy, To regroup numbers you first add the ones and in this case its 28 + 5 so 8 + 5 is 13 then you take the tens out of the 13 and add that to the 20 thats left over 20 + 10 is 30 then take the 3 and add that to the 30, 30 + 3 is 33 there Ya Go