Total Work = Time × Efficiency Calculation: Let total work = LCM 22=22 units (for easy calculation) Efficiency of A=22 ÷ 22=1 unit/day Since A and B work alternately starting with B, in 11.5 days: B works on Day: 1,3,5,7,9,11⟶6 full days A works on Day: 2,4,6,8,10, and 0.5 of Day 12⟶5.5 days A's total work =5.5×1=5.5 units Remaining work =22−5.5=16.5 units This 16.5 units is done by B in 6 days ⇒ B's efficiency =16.5÷6=2.75 units\/day Now, we need to find the time taken by B alone to complete 3∕4 of the original work: 3/4 of 22=16.5 units ⇒ Time =16.5÷2.75=6 days