Question

I really need help on geometry

Answer 1

For example, exc. 15.

x + y = 10 and 6/x = 9/y; You need y!

=> x = 10 -y and 9x = 6y => 9(10-y) = 6y => 90 - 9y = 6y => 15y = 90 => y = 6.