To find the constant of proportionality for the number of minutes it takes Cameron to read 1 page, we start with the information given: Cameron reads 15 pages in 60 minutes.
To find out how many minutes it takes to read 1 page, we can set up a ratio:
\[ \text{Minutes per page} = \frac{\text{Total minutes}}{\text{Total pages}} = \frac{60 \text{ minutes}}{15 \text{ pages}}. \]
Calculating this gives:
\[ \text{Minutes per page} = \frac{60}{15} = 4 \text{ minutes per page}. \]
Therefore, the constant of proportionality for the number of minutes to read 1 page is:
C. 4