For two one-year fixed periods, 4000*( 1+0.0225) in the first year is the sum of principal and interest in the first year, and 4000 * (1+0.0225) * (1+0.0225) is two years, and the result is 4/kloc.

Two-year fixed term, 4000 * (1+0.0279 * 2) = 4223.2, so it seems that it is cost-effective to save for two years.

The second question:

Assuming that the unit of commodity cost is "1", then the selling price of commodity is 1*( 1+0.2), that is 1.2 * 0.88 =1.