42*25= 1050

2. Store B: 50*20= 1000

3. Point C 50*25= 1250 yuan

Every 100, returns 20, 1250. If 50 is removed, it is less than 100, and the remaining 1200 is greater than 100, and returns 100 * 20 = 240.

Actual cost1250-240 =1010 yuan.

So store b is the most affordable.