Number 6's attempt is wrong because the perimeter of a rectangle has 4 sides, not two. It should look like:
[tex]P = 200+200+150+150=700[/tex]
Number 7 is wrong because it calculated the area by multiplying.
(Bonus: Number 7 would be right if they were laying down dirt in a 200 by 150 field at ten bucks per square foot...)
