You find it by dividing one number by another and take it from there. Example:
If a farm had 100 rabbits last year and this year that number is 110 rabbits, what is the instantaneous rate of change? This is how it is calculated:
110/100 =1.10 - 1 x 100 =10% change in 1 year.
Now, we take the natural log of 1.10:
ln(1.10) =0.0953 x 100 =9.53%, which is the instantaneous rate of change.