400 miles cannot be correct, for 30 cents times 
400 miles gives $120. And $65 times 3 days gives $195. 

But adding $195 + $120 gives $315, not $275.

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Just think how the total bill was figured.  It was this way:

1.  $65 TIMES THE NUMBER OF DAYS 

PLUS 

2.  $0.30 TIMES THE NUMBER OF MILES

EQUALS

3.  THE TOTAL BILL 

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Let's look at 1.  That's $65 times 3 days or $195.

Let's look at 2.  We don't know the number of miles, so we let
the letter x represent this unknown number.  But we can
multiply $.30 by x anyway and get $.30x

Let's look at 3.  That's given as $275.

So we have

$195 PLUS $.30x EQUALS $275

or dropping the dollar signs, and using + for PLUS and = 
for EQUALS:

195 + .30x = 275

Now we subtract 195 from both sides:

      .30x = 80

Now we divide both sides by .30



       

So it's not 400 miles, it's 266.67 miles.

Edwin