A certain rectangular window is three times as long...

[BTGmoderatorLU]

A certain window is three times as long at it is wide. If its perimeter is 28 feet, what are its dimensions in terms of length by width?

A. 12 by 2
B. 11 by 3
C. 10.5 by 3.5
D. 10 by 4
E. 9 by 3

The OA is C.

I'm really confused with this PS question. Experts, any suggestion? I don't undestarnd it.

I know that its perimeter will be, P = 2L + 2W = 28, also I know that L = 3W. But I don't have it clear, what can I do for solve it. Thanks in advance.

[Brent@GMATPrepNow]

A certain window is three times as long at it is wide. If its perimeter is 28 feet, what are its dimensions in terms of length by width?

A. 12 by 2
B. 11 by 3
C. 10.5 by 3.5
D. 10 by 4
E. 9 by 3

The OA is C.

I'm really confused with this PS question. Experts, any suggestion? I don't undestarnd it.

I know that its perimeter will be, P = 2L + 2W = 28, also I know that L = 3W. But I don't have it clear, what can I do for solve it. Thanks in advance.

Let's continue where you left off.
You have:
2L + 2W = 28
L = 3W

Take the top equation and replace L with 3W (from 2nd equation) to get: 2(3W) + 2W = 28
Expand: 6W + 2W = 28
Simplify: 8W = 28
So, W = 28/8 = 3.5

Check the answer choices.....only one answer choice has 3.5 as one of the dimensions, so the correct answer is C

That said, we can easily find the other measurement.
Since W = 3.5, and since we already know that L = 3W, we can plus W = 3.5 into the equation to get: L = 3(3.5) = 10.5

So, the dimensions are 3.5 by 10.5 (answer choice C)

Cheers,
Brent