Monthly fixed cost = 3000+8000+1000 =11000.

Monthly guaranteed sales turnover =11000/62.5% =17600 yuan.

Monthly guaranteed sales volume = 17600/4=4400 copies.

Daily guaranteed sales =4400/30= 146.7 copies.

If you want to repay the capital in half a year, amortize the investment of 40,000 yuan to six months, that is, 40,000/6+17600 = 24,266 yuan, and you can only repay the capital in half a year, with a monthly sales volume of 6,067 copies.

The data you gave is unprofessional, and the net interest rate can't be accurate. I'll give you an industry reference value. The average net interest rate of fast food is around 10- 18%, because your costs include amortization, demolition, advertising, taxes and fees, losses, low-value consumables and miscellaneous expenses.