So we want to know what is the money lost or profited in the 4 year period of the store if the money lost for two years was 13000$ and 21000$ and money profited was 129000$ and 310000$. To get the answer we simply add the annual losses and profits: -13000$-21000$+129000$+310000$=405000$. So after 4 years the overall profit is 405000$.