Answer:
The rules of significant figures are as follows;
1) Significant figures are the first digit in the number that isn't a '0'. Doesn't matter how far behind or in front of the decimal point it is.
1st Significant figure of 5098 is 5000. The first number that isn't a '0'.
When you get onto the 2nd is when it gets confusing. After the first significant figure, any number which comes after it is a significant figure regardless of whether it is a Zero.
Thus the second significant figure of 5098, is 5000 too.
And the third? Well, it's the third number in.
So the third is 5090.
In addition, you add significant figures like any other number. Due to the fact that it is rounded off, however, it will not be exact.