Call the width x. Note that the length is 3x-6. We know that double the width plus double the length is 120, so we write an equation:
[tex]2(x)+2(3x-6)=120[/tex]
[tex]2x+6x-12=120[/tex]
[tex]8x-12=120[/tex]
[tex]8x=132[/tex]
[tex]x=16.5[/tex]
If x is 16.5, the width is 16.5, and the length is [tex]3 \cdot 16.5 - 6 = 43.5 [/tex].
