Answer:
1.2 × 10⁸ m
Explanation:
You want to convert metres to nanometres.
Recall that the multiplying prefix nano- means × 10⁻⁹, so
1 nm = 1 × 10⁻⁹ m
The conversion factor is either [tex]\frac{\text{1 nm} }{10^{-9} \text{m}}[/tex] or [tex]\frac{10^{-9} \text{m} }{\text{1 nm}}[/tex].
You choose the one that has the desired units (nm) on top. Then
[tex]\lambda = \text{0.12 m} \times \frac{\text{1 nm} }{10^{-9} \text{m}} = 1.2 \times 10^{8} \text{ nm}[/tex]