To find out how much the saleswoman should return to her, we have to find out how much Sara spent in total. She spent 5.5£ + 6.5£ = <<5.5+6.5=12>>12£.
So she gives 20£ and the cashier should keep 12£. The cashier therefore returns the difference between these two sums: 20£ – 12£ = <<20-12=8>>8£
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