3 sisters bought 2 x 3 = 6 dress and and 1 x 3 = 3 purses.
3 sisters bought 6 dresses and and 3 purses.
Find 3 purses:
1 purse = $26
3 purses = $26 x 3 = $78
Find 6 dresses:
Total = $205.50
6 dresses = $205.5 - $78
6 dresses = $127.50
Find 1 dress:
6 dresses = $127.50
6 dresses = $127.50 ÷ 6
1 dress = $21.25
Answer: $21.25