Here’s some homework

I promised myself I would sit down and write an entry when I got done with my Algebra homework. 
However, I can’t seem to finish it.  One problem I just gave up on, and will ask the Instructor tomorrow.
The other one, maybe you can help me with. 
It is dear to my heart, because I have been known to crochet yards of lace.

Problem:
To trim the edges of a rectangular tablecloth, 42 feet of lace are needed.  The length of the tablecloth is exactly one-half its width.  What are the dimensions of the tablecloth?
I peeked back at the answers, and once I know that, it all makes sense.  I cannot figure how it comes about.

formula:  the perimeter = 2 times length plus 2 times width

Answer:  7 feet by 14 feet ( length = 7 feet; width = 14 feet)

Update:  18Feb05

I asked the Instructor this morning about the formula.
I cannot write all the symbols but it goes something like this

P = 42
x = biggest number because it doesn’t matter where the numbers fit, they are multiplied the same

2(x) + 2 (1/2 x) = 42
2 x + x = 42
3x = 42
divide each side by 3
x = 14
1/2 x = 7
 
Whew!  crocheting the lace is easier…..