The Homework Thread

[Spudman]

Originally Posted by Julia B

I've seen a couple threads about different homework assignments, so I decided to make this one to use for all homework instead of creating tons of specific threads. Please don't post, "hay guyz, plz rite a essay 4 me. thx."

I'm having trouble with a math problem:
A satellite camera takes a rectangular-shaped picture. The smallest region that can be photographed is a 5-km by 7-km rectangle. As the camera zooms out, the length L and width W of the rectangle increase at a rate of 2 km/sec. how long does it take for the area A to be at least 5 times its original size?

This is what I have so far:
A=L*W
A=(5+2s)(7+2s)
If the area needs to be 5 times larger than 35...
175=(5+2s)(7+2s)
175=35+24s+4s^2
140=4s^2+24s
35=s^2+6s

How do I get past this?

With the quadratic formula of course: http://en.wikipedia.org/wiki/Quadratic_equation