How many years are between the loss of the serbs and the persians

1868 years.

Explanation:

The Persians lost against the Greeks in 479 BCE (which stands for Before Common Era or Before Christ). On the other hand, the Serbs were conquered by the Turks in 1389 CE (Common, modern Era).

Since these two events happened in different eras (before and after Christ), in order to calculate how many years have passed between them, we need to add those two numbers: 479 + 1389 to get 1868.

c) troops march forward in close formation against newer, more accurate weapons