1. 20.93 is 7% of something. Divide 20.93 by 7 and you get 2.99, which is 1% of something Multiply 2.99 by 100 to get the original value, $299
2. 5.5% of 5700 is 313.5. Add that to 290 to get $603.5
3. The $375 that she earns is 5% of what she has sold. Multiply 375 by 20 to get $7500, how much she needs to sell
4. The total cost of the 3 lamps is 22.49x3, 67.47. Add that to 829.99 to get 897.46. Multiply that by 0.0425 (4.25%) to get 38.14205, or just 38.14 in sales tax