Can yall help solve this I'll give brainliest ​

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )

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

Need plz been trying to do it for a long time and still haven’t succeeded