To make $4,500 in a single week, Norma needs to earn a total of:
$4,500 = (total earnings from hourly pay) + (total earnings from commission)
Let's first calculate Norma's total earnings from hourly pay:
(total earnings from hourly pay) = (hourly rate) x (number of hours worked)
(total earnings from hourly pay) = $25/hour x 35 hours/week
(total earnings from hourly pay) = $875/week
Now, let's calculate the total amount of sales she needs to make to earn $4,500:
(total earnings from commission) = (total sales) x (commission rate)
(total earnings from commission) = (total sales) x 0.15
(total sales) = (total earnings from commission) / 0.15
(total sales) = ($4,500 - $875) / 0.15
(total sales) = $3,625 / 0.15
(total sales) = $24,166.67
Therefore, Norma needs to make $24,166.67 in sales to earn $4,500 in a single week, assuming she works 35 hours and receives a commission rate of 15%.