What is the algebraic solution and expression for this question: a stray dog 812 of your muffins. that was 3/10 of all of them! with how many did you start

You would first put 3/10 as a decimal: 0.3
Then you know there's a remaining 7/10 somewhere
You then put that as a decimal: 0.7
After that, you multiply 812 by 0.7  which would give you the 7/10 missing
Add those together and you get your 1380.4 muffins