Solution:
Given that Frank and Janny both bought a $40 scooter.
Frank sold hers to a friend for 15% less than the original price.
This implies Frank sells it for 85% (that is 100% - 15%)
Frank selling price = 0.85 x 40 = $34
Janny sold hers for 30% less than the original price.
This implies Janny sells hers for 70% (that is 100% - 30%)
Janny selling price = 0.7 x $40 = $28
Thus, The amount Frank get for her scooty than Janny = $34 - $28 = $6
The answer is $6