Answer
A $300\%$ increase in wavelength is required.
Work Step by Step
We can find $\Delta \lambda$:
$frac = \frac{\Delta \lambda}{\lambda + \Delta \lambda} = 0.75$
$\Delta \lambda = (0.75)(\lambda + \Delta \lambda)$
$0.25~\Delta \lambda = 0.75 \lambda$
$\Delta \lambda = 3.0 \lambda$
Therefore, a $300\%$ increase in wavelength is required.
