Official guide 13-prob 62...Please explain on how to think

[Divya Ann Chacko]

Stores L and M each sell a certain product at a different regular price. If both stores discount their regular price of the product, is the discount price at Store M less than the discount price at Store L?
1) At store L the discount price is 10 percent less than the regular price: at store M the discount price is 15 percent less then the regular price
2) At the store L the discount price is $5 less than the regular store price: at store M the discount price is $6 less than the regular price.

[GMATGuruNY]

Stores L and M each sell a certain product at a different regular price. If both stores discount their regular price of the product, is the discount price at Store M less than the discount price at Store L?
1) At store L the discount price is 10 percent less than the regular price: at store M the discount price is 15 percent less then the regular price
2) At the store L the discount price is $5 less than the regular store price: at store M the discount price is $6 less than the regular price.

Each statement alone is clearly insufficient.

Statements combined:
At Store L, the $5 discount is equal to 10% of the regular price:
5 = .1x
x = 50.
Thus, the discount price at Store L = regular price - discount = 50-5 = 45.

At Store M, the $6 is equal to 15% of the regular price:
6 = .15y
y = 40.
Thus, the discount price at Store M = regular price - discount = 40-6 = 34.

Result:
The discount price at Store M is lower.
SUFFICIENT.

The correct answer is C.