2(11/35) + 5/21 - 17/35

= 22/35 + 5/21 - 17/35

= (223)/(353) + (55)/(215) - (173)/(353)

= 66/105 + 25/105 - 51/105

= (66 + 25 - 51)/105

= 40/105

= 8/21

Поэтому, при b = 11/35, 2b + 5/21 - 17/35 равно 8/21.