Note that Rom used engineering notation to depict the numerical values. Engineering notation is a specialized subset of scientific notation, and its use is common (and preferred) in all branches of physical sciences.
Reviewing this will help you understand the (different) notations presented by Rom and Melody
https://en.wikipedia.org/wiki/Engineering_notation
Start by familiarizing yourself with the eight prefixes that modify the unit value:
Observe that engineering notation uses base 1000; here it’s contrasted to base 10 used in standard scientific notation.
tera T 10004 1012
giga G 10003 109
mega M 10002 106
kilo k 10001 103
UNIT 10000 100
milli m 1000−1 10−3
micro μ 1000−2 10−6
nano n 1000−3 10−9
pico p 1000−4 10−12
Having an instant working knowledge of these prefixes will help you understand these questions.
Another note:
Also, in the Wiki article pay attention to the overview, starting with:
“... Compared to normalized scientific notation, one disadvantage of using SI prefixes and engineering notation is that significant figures are not always readily apparent. ...” Note in the text, following this extract, that the speed of light is used specifically as an example for significant figures.
The speed of light constant is used in your question, and though significant figures is not an explicit concern for your presented question or its solution, it is always an implied concern. An understanding of significant figures for constants and measurements will quickly become significant as you pursue your studies in physics.
Other general helps for learning physics:
Learn the Greek alphabet and the context in which the symbols are used (in mathematics and physics). In your question, the Greek letter \(\lambda\) (lambda) is used and its context means Wave Length. The Latin letter (c) is used to denote the constant for the speed of light in a vacuum.
Remember this constant (c) is speed of light in a vacuum; when light passes through other media, it slows down, and further, it slows down in proportion to its frequency (wave length). This is why you can see “rainbow” colors when composite (white) light passes through the atmosphere or a prism.
Another thing to remember is “light” in this context refers to the full electromagnetic radiation spectrum, not just the small portion that is visible.
GA