Using proportions, it is found that the equation that can be used to find the number of emails he marked as important is:
n = 0.12(125)
What is a proportion?
A proportion is a fraction of total amount.
In this problem, the total amount is the 125 e-mails, while the fraction is 12%, hence:
[tex]n = \frac{12}{100} \times 125 = 0.12(125)[/tex]
Hence, the equation is n = 0.12(125).
You can learn more about proportions at https://brainly.com/question/26509024