What the answer and how can i explain my answer

The order of operations, is PEMDAS (parentheses, exponents, multiplication, division, addition, subtraction) so you should always follow that order when you're solving equations like this one, but when it comes to multiplication and division, it just depends on whichever one comes first, and the same is true for addition and subtraction. So since there aren't any parentheses or exponents here, we will start with multiplication or division...it just depends on which one comes first in the equation. 15 ÷ 3 is first so we start with that: 15 ÷ 3 = 5:
5 + 6 x 2 - 10 = ?     Now we move onto the next multiplication or division problem we see until there are no more left. 6 x 2 is the next and last one:
6 x 2 = 12           5 + 12 - 10 = ?      Now we move on to addition and subtraction, and again, whatever comes first is what we do first:
5 + 12 = 17      17 - 10 = ?     Last but not least:    17 - 10 = 7

So your answer is 7! Hope this was helpful!