Given:
Marked price = 7500
First discount = 18%
He offers a further discount of 10% if the buyer returns his old vacuum cleaner
Formula used:
Marked Price (100-discount)% = Cost Price(100+profit)%
Calculation:
Cost price is 30% less than Marked price
Cost Price = 7500 × 10070
= 5250
Step 1:Profit With return(P1)
Marked Price (100 - discount)% = Cost Price (100 + profit)%
7500 (100 -18)% (100 -10)% = 5250 (100 + P1)%
7500 × 10082 × 10090 = 5250 100100+P1
5535= 5250 100100+P1
5250553500= 100 + P1
5250553500−525000 = P1 = 525028500
Profit% of the retailer with the return of the old vacuum cleaner scheme = 5.43%
Step 2:Profit Without return (P2)
Marked Price (100-discount)% = Cost Price(100+profit)%
7500 (100-18)% = 5250 (100+profit)%
7500 × 10082 = 5250 100100+profit
6150 = 5250 100100+profit
5250615000 = 100 + profit
5250615000−525000 = 525090000
Profit% of the retailer with the return of the old vacuum cleaner scheme = 17.14%
*Step 3:*The profit of the retailer with the return is what percentage of the profit without the return
= 9000028500 × 100
= 31.66
Approximately 32%
Answer is 32%.

Alternate MethodGiven:
Marked price = 7500
First discount = 18%
He offers a further discount of 10% if the buyer returns his old vacuum cleaner
Formula used:
Successive discount = Discount 1 + Discount 2 - 100Discount1×Discount2
Profit = Cost Price(Selling Price−Cost price) × 100
Selling Price =( 100 - Discount )% Marked Price
Calculation:
According to the question only percentage is asked so don't take the amount in consideration
Let 100 be the Marked Price and 70 be the Cost Price
Step 1:Profit With return
Successive discount = Discount 1 + Discount 2 - 100Discount1×Discount2
= 18 + 10 - 180/100
= 26.2%
Selling Price =( 73.8 )% × 100
= 73.8
Profit = 70(3.8) × 100
= 738
Step 2:Profit Without return
Selling Price =( 100 - 18 )% × 100
= 82
Profit = 70(12) × 100
= 7120
*Step 3:*The profit of the retailer with the return is what percentage of the profit without the return
= 12038 × 100
= 31.66
Approximately 32%
Answer is 32%.