An item is regularly priced at $39. Ashley bought it at a discount of 55% off the regular price.

Ashley bought the item for $17.55

55% off the regular price means she paid 45% of the regular price. (100% - 55% = 45%

Multiply the original price by 45%:

39 x 0.45 = 17.55

She paid $17.55

(If you need to know how much she saved: 39 - 17.55 = $21.45)