First, we should have it in a way that is visually easier to understand:
We first multiply the first two terms in the analysis:
Notice that the 100.0 lost it's 0 because 1.00 has 3 significant digits and therefore 100 also has to have three sig digs, since 100.0 has 4 significant digits, then we keep the decimal and lose the zero to get 3 significant digits. Now we multiply the other two numbers:
You can use 2860 because both 100. and 28.6 have 3 significant digits, and 2860 has 3 as well, therefore the answer works.