Describe a compound event that has a probability between 50% and 80%

Mexico city, mexico, is the world's second largest metropolis and is also one of its fastest-growing cities with a projected growth rate of 3.2% per year. its population in 1991 was 20,899,000 people. use the formula p = 20.899e0.032t to predict its population p in millions with t equal to the number of years after 1991. what is the predicted population to the nearest thousand of mexico city for the year 2010?

Could somebody me with this radical simplification?

Cd is the perpendicular bisector of both xy and st, and cy=20. find xy.