Can someone explain were do they get the number 2.99 and 10^8?

In standard decimal notation, the speed of light is 299,800,000.0 meters per second. In scientific notation this is written as 2.998x108 meters per second, meaning that the true position of the decimal point is 8 digits to the right. In this case, that means filling in the empty spots with zeros.

Hope it helped

its first and third is your answer i did the qustion the fourth isnt right