If a country has falling birth rates, what would the government want to do in terms of migration? Will they want to force people in to the country? Force people out? What about xenophobic governments such as Japan?

You need to re ask the question with proper

You're asking in the ap section, so i'll give the ap calculus-style answer. alternatively, you can find the vertex of the parabola and use the "y"-coordinate as the answer.

the maximum height can occur at a critical number, that is, a number  such that  .

the derivative of  can be calculated as follows:



find a value of  that is a zero of the derivative:


this is parabola that is opening downward; we can assume there is a maximum at  .

to find that maximum, calculate  .

At 8.5% i am making after one year 1,500   +  1,500 x 0.08 = $1,620

my credit card cost 1,600 + 1,600 x 0.19 = $1,904


total balance =  interest  (negative)  of credit card + interest earn (positive)

that is  -304 + 120 = -$181