Please, explain me why an answer is 12

Question

https://code.sololearn.com/WX59p73Qr2xm/?ref=app

Answer 1

1 += 2.5 + 1 +1 //a=5.5, b=c=2
5.5 += 2.5 + 2 + 2 // a=12, b=c=3

Answer 2

Юлия, спасибо, забыл заменить новые значение на старое)

Answer 3

Пожалуйста)

Answer 4

Because you BELIEVEEEEEED IT TO BE SO, mannnnnn