Astore is having a 20%-off sale on all merchandise. if mai buys one item and saves $13, what was the original price of her purchase?

This is so harddd! solve. 1 + 1 = solve 4 + 4 = solve 3 x 3

Need ! give step by step solutions on how to solve number one \frac{9-2\sqrt{3} }{12+\sqrt{3} } number two x+4=\sqrt{13x-20} number three (domain and range) f(x)=2\sqrt[3]{x} +1

Bob is putting books on a shelf and takes a break after filling 18 1/2 inches on the book shelf. the book shelf is now 2/3 full. how long is the entire bookshelf?