Maths Question

Today for maths me and my friends all got different answer on one of our questions. The question was  " 6.4 + 8.7 = " Me and my friends all got different answers someone got 2.5 and someone else got another answer. In the end we all ended up getting the same answer we ended up getting 15.1 and this is how we got our answer.

We added up all the tenths  in the numbers 8.7 and 6.4 which would be .7 and .4 . We added up these two numbers because we were all trying different ways to get the same answer. The answer to .7 + .4 = 1.1 and then we moved onto adding up the whole numbers which were 8. and 6. We took away one whole from eight and added it to the 6 wich made seven. And then we had 7 and 7 left so we added them up wich made fourteen and 14. + 1.1 = 15.1. Something that I got from doing this question was to work with other people and come together to try and get an answer that we all agree on.