Can anybody help explain this?

With: label the vertices and all the elements needed. find x

12. the amount of money in a bank account decreased by 21.5% over the last year. if the amount of money at the beginning of the year is represented by ‘n', write 3 equivalent expressions to represent the amount of money in the bank account after the decrease?

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