The formula for area is as follows:
[tex] area = length * height [/tex]
Of course length or height could be substituted for width as well.
Our width is [tex] 9 ft [/tex], our height is [tex] 5 ft [/tex]. So multiply [tex]9[/tex] by [tex]5[/tex], and our answer is [tex]45 ft^{2}[/tex]
Make sure you keep your units, they're important!