You assume exponential growth. This means that the rate of change of the population is an exponenbtial, in pathematics terms, with P being the population

. To solve for your two constants, you use the conditions given. Taking the zero time to be 1970 gives

. This gives A. Then, after 25 years (1995), you have

. Solve for R.

For the percentage change, consider that if the function is not thought of as continous, then it can be written discretely as

Use the function to get the change between 1975 and 1970. Divide by 5 to get the average. etc.