We need to identify the amount of significant figures in the number 9.79.
Significant figures or significant digits are digits in the number that are reliable and necessary to indicate the quantity of something. For example: if one balance provides us with the mass "1.5 g" and a second balance provides the number "1.5167 g", the first balance presents a measurement with 2 significant digits and the second one, 5 significant digits. This means that the second balance is able to provide a measure with more resolution.
We consider significant figures in a number all digits that are required to idicante the quantity it is referring to. The number 9.79 presents 3 significant digits (9, 7 and 9).