How do I send pictures?

The depth of a lake at a certain point, wich is a function of the distance of that point from shore, is 30 feet.

If f(x)=2x-6 and g(x)=3x+9, find (f-g)(x)

7. if the value of x varies directly with the value of y, and x = 3 when y = 21. what is the valu y, and x = 3 when y = 21. what is the value of x when y = 105?