The usual price of a file sold at Shop U and V is $20. During a sale, a discount of 25% is given to every file sold at Shop U. At Shop V, a discount of 40% is given to the 4th file for every 4 files sold. How much cheaper would it be if Vanessa buys 15 files from Shop U instead of Shop V?

	Shop U	Shop V
Price of 1 file	75%  $15	100% $20
Every 4th file		60% $12

Price of 1 file from Shop U in percentage
= 100% - 25%
= 75%

Price of 1 file from Shop U at 25% discount
= 75% x 20
= ⁷⁵₁₀₀ x 20 
= $15

Cost of 15 files from Shop U
= 15 x 15
= $225

Price of the 4th file from Shop V in percentage
= 100% - 40%
= 60%

Cost of 4th file at Shop V
= 60% x 20
= ⁶⁰₁₀₀ x 20 
= $12

Cost of 1 set of 4 files at Shop V
= 20 x 3 + 12
= $72

Number of sets of 4 for files at Shop V
= 15 ÷ 4
= 3 r 3

Cost of 3 sets of 4 files at Shop V
= 3 x 72
= $216

Cost of 3 files at Shop V
= 3 x 12
= $36

Cost of 15 files at Shop V
= 216 + 36
= $252

Amount cheaper if Vanessa buys 15 files from Shop U instead of Shop V
= 252 - 225
= $27

Answer(s): $27