Joan joined her school's band. She bought a viola for $72.21, and a song book which was $7.25 with a $100 bill. How much change was Joan given?

Me because some of question i don’t understand

Arley is building a model of a city map. in one part of the city, three roads form a right triangle, which harley draws as triangle abc, with the following measures: m∠b=90° and m∠a=30°. in his scale model, the hypotenuse of triangle abc, ac¯¯¯¯¯¯¯¯, has a length of 817−−√ cm. what is the value of a (the length of bc¯¯¯¯¯¯¯¯)?

Which equation represents h for right triangle abc