Find the difference. express your answer in simplest form. (4r/s) - (r/s)

For this case we have the following expression:
 (4r / s) - (r / s)
 We observe that we have the term r / s in the whole expression.
 Therefore, we can draw common factor.
 Rewriting we have:
 (r / s) * (4-1)
 (r / s) * (3)
 3 (r / s)
 
 the difference is:
 3 (r / s)

The answer would be 13.5 minutes.

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