13. which equation is equivalent to 8x + 4y = -24?

Asocial networking site currently has 400,000 active members, and that figure is predicted to increase by 32% each year. the following expression represents the number of active members on the site after t years.

What are the coordinates of the midpoint of ab? ,1/2) /2,-1) ,-3/2) /2,-2)

How is this equation completed? i cannot find any examples in the book.