The number of days that Sydney can afford to rent while staying within her budget is 3 days.
Total budget  ≤ (total number of days x cost per day) + (cost per mile x total mile)
$260 ≤ $77.50xx + ($0.10 x 275)
$260 ≤ $77.50xx + 27.50
$260 - 27.50  ≤ $77.50xx
232.50  ≤ $77.50xx
xx  ≤  232.50 / $77.50
xx  ≤ 3
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