Help on geometry homework?

[jaqueline_nguyen]

This is on ch.9 and how do you find the value of each variable?and how do you solve a proportion like:

12.)8 over 4 equals something over x
13.) 9 over x equals x over something
14.)8 over x equals x over something

15.)ad over cd equals something over db
16.)eg over fg equals fg over something
17.)ij over ik equals something over il

1.)ad=16, db=12,dc=?
2.)ab=20,ad=16,ac=?
3.)ad=16,dc=2,bc=?
4.)dc=4,bc=6,ac=?
5.)ad=25,db=10,dc=?
6.)ad=4,dc=1,db=?

12.)ad over cd equals ac over bc is that true or flase?
13.)Is Df an altitude of triangle adc?
14.)ce over cb equals cf over ca is that true or false?

Solve proportion:
15.)x over 12 equals something over 8
16.) 15 over x equals x over something
17.)9 over x equals x over something