How did the author of a textbook arrive at 42% in this problem?

Question

The laboratory’s range is 2.3 to 4.2

The blood test result is 3.1

The textbook says 3.1 is 42% of the range.

How did the author arrive at 42% ?

Answer 1

4.2-2.3=1.9

3.1-2.3=.8

.8/1.9=42.1%

To get a %; just divide. 6 is ----% of 3? 6/3=2; move the decimal.