Answer
The correct answer is:
C. $6.0~m$
Work Step by Step
We can write two expressions for $L$:
$L = \frac{n\lambda_n}{4} = \frac{(n)(8)}{4} = 2n$
$L = \frac{(n+2)~\lambda_{n+2}}{4} = \frac{(n+2)(4.8)}{4} = 1.2~n+2.4$
We can equate the two expressions to find $n$:
$2n = 1.2n+2.4$
$0.8n = 2.4$
$n = 3$
Then: $~L = 2n = (2.0~m)(3) = 6.0~m$
The correct answer is:
C. $6.0~m$
