1/4 + 2/7 + 11/12 subtract 3/4

Answer 1

how come you can say + but cannot say - ????

1/4 + 2/7 + 11/12 - 3/4
= 2/7 + 11/12 - 1/2
= 24/84 + 77/84 - 42/84
= ...