If we multiply each by 4/3, we can look to see which is closest to 1. This step is not strictly necessary, but it is often easier to compare to 1 than to compare to 0.75.)

30/42*4/3 ≈ .95238 (differs from 1 by .04762)

15/19*4/3 ≈ 1.05263 (differs from 1 by .05263)

45/63*4/3 ≈ .95238 (this is an equivalent to the first fraction)

39/51*4/3 ≈ 1.01961 (differs from 1 by

63/86*4/3 ≈ .97674 (differs from 1 by .02326)

The closest value to 3/4 is

30/42*4/3 ≈ .95238 (differs from 1 by .04762)

15/19*4/3 ≈ 1.05263 (differs from 1 by .05263)

45/63*4/3 ≈ .95238 (this is an equivalent to the first fraction)

39/51*4/3 ≈ 1.01961 (differs from 1 by

**.01961**)63/86*4/3 ≈ .97674 (differs from 1 by .02326)

The closest value to 3/4 is

**39/51**= 13/17