A room is 15 feet tall. An architect wants to include a window that is 6 feet tall. The distance between the floor and the bottom of the window is b feet. The distance between the ceiling and the top of the window is a feet. This relationship can be described by the equation
a
=
15
−
(
b
+
6
)
a=15−(b+6).

The customer wants the window to have 5 feet of space above it. Is the customer describing a or b? What is the value of the other variable?