The exponential function is given in the form

where a is the initial value and b is the multiplicative rate of change
So lets plug the first two values of the table in this function , we get
or

Now plug second

Divide equation 2 by equation 1

On simplifying we get

or

So the multiplicative rate of change of the function is

Rounding numbers means you change the number to a closer, easier number. For example if you want to round 56 to the nearest tenth, it would round to 60.
Estimating numbers is when you guess numbers. For example, if you want to estimate the measure used to measure a bed, i would estimate feet.
I hope this helped:))