1) The work efficiency of Party A and Party B is 1/4 and that of Party B and Party C is 1/5.

Therefore, the working efficiency of A, C and B is 1/4+ 1/5=9/20.

So 9/20 * 2 = 18/20 A, C and two B work for two hours.

So the remaining1-18/20 =110.

So the remaining110 is made by Party B alone, and it takes 6-2*2=2 (hours).

So B needs 2 divided by110 = 20 (hours) to complete this project alone.