PLEASE HELP ME KIND SOUL! Look at the picture below to understand everything

Hey! How are you?

So the problem is below and I have found an answer online, BUT the issue I am having is this:
I do not think the given answer is the largest possibility. Since 6 is the largest number, can’t I just use that and get a sum of 509.04 > 368.24
Pretty please help me! I am begging you, I have lost all my brain cells, please clear VERy clear explanations needed!!!