Step 1: Move the decimal point from its current position (the black dot) to a position immediately to the right of the first nonzero digit (the red dot).
1.531.57899
Step 2: We moved the decimal point 3 spaces to the right. Therefore, the exponent on base 10 will be positive 3.Now we know that the:
Mantissa = 1.53157899
Exponent = 3
So, the solution is:
$$1531.57899 = \color{blue}{ 1.53157899} \cdot 10^{ \color{red}{ 3 }}$$