The cooperation between two people is 2/15+1/6 = 9/30 = 3/10.
1.( 1-2*2/ 15)/(3/ 10)=22/9
2. Leave Party A alone for x hours and Party B alone for y hours, together (4-X-Y).
X * 2/ 15+Y * 1/6+(4-X-Y)* 3/ 10 = 1
4X+5Y+9(4-X-Y)=30
6=5x+4y
y=(6-5x)/4
Where x is greater than or equal to 0 and less than or equal to 6/5.
Answer: Party A can work alone for X hours, while Party B can work alone for (6-5X)/4 hours and work together for (10+x)/4 hours.