(1) unit price x of repeater and unit price y of schoolbag, and establish equations:

x+y = 440

4y-x = 10

So, x=350, y = 90.

(2) The price of a supermarket repeater after 15% discount is 350*0.85 = 297.5, and the price of schoolbags after 20% discount is 90*0.8 = 72. It costs 297.5+72 = 369.5 yuan to buy together;

Supermarket B returns to 0 yuan after 50 days, and to 80 yuan after 440 days, so the total price is 440-80 = 360 yuan, so it is more economical to buy in supermarket B, saving 369.5-360=9.5 yuan.

I hope it will be adopted. Thank you.