3/4-9/28+12/70-18/130+21/208
=21/28-9/28+12/70-18/130+21/208
=3/7+12/70-18/130+21/208
=30/70 +12/70-18/130+21/208
=6/10-18/130+21/208
=78/130-18/130+21/208
=6/13 + 21/208
=96/208 + 21/208
=117/208
=9/16