Final answer:
To find Susan's profit, we subtract her costs from her total sales revenue. With an expenditure of $20 and sales totaling $38.40 from 12 bracelets, her profit is $18.40. The portion she sets aside for next month would depend on the specific percentage she chooses.
Step-by-step explanation:
The subject of the question involves basic arithmetic and the concept of profit calculation in a business scenario. To calculate Susan's profit from selling bracelets, we subtract her initial costs from the revenue she generated. If Susan spent $20 on supplies and sold 12 bracelets at $3.20 each, her revenue from sales is 12 x $3.20 = $38.40. The profit would thus be $38.40 - $20 = $18.40. To determine the portion of her profit she plans to set aside for supplies next month, we would need to know the specific percentage Susan has decided on. Without this information, we can't calculate the exact amount.