SARS-CoV - relative size of the spike protein
Although this is a homework question, I also think OP deserves a help as orthocresol suggested. I'm not going to go into details but leave it at orthocresol's suggestion of this being a Western Blot of protein analysis, which is absolutely correct. Hence, OP should start reading of electrophoresis and western blots techniques since, I assume, s/he taking molecular biology class.
In brief, the given image is a X-ray photograph of the nitrocellulose membrane after transferring the proteins from the SDS-PAGE gel (after electrophoresis). I'm suggesting that because the image looks like visualized by radioactivity (I suggest OP to read about these techniques in details to understand). In SDS-PAGE gel electrophoresis, the proteins separated mainly by molar mass of each protein while heaviest protein go first since electric current run from top to bottom as sepicted in following diagram:

As marked in the diagram, SARS-CoV consists of SARS-M ($\pu{20 kD}$, SARS-N ($\pu{54 kD}$, and SARS-S (~$\pu{175 kD}$ proteins. I may give you your answer but I strongly suggest to read about the subject for better understanding. I do not support online courses, but there are no choice you can made during a bad pandemic era.