2X-8=0.5(X+8)+9
2X=0.5X+4+ 17
4X=X+42
3X=42
X= 14
The number of people in group B is 14.
It is estimated that it will take x hours to complete.
1/ 15+4 * 1/ 12+X *( 1/ 15+ 1/ 12)= 1
1/ 15+ 1/3+X[(4+5)/60]= 1
6/ 15+X[3/20]= 1
2/5+X[3/20]= 1
X[3/20]=3/5
X=(3/5)/(3/20)
X=(3/5)*(20/3)
X=4
It will take another four hours to finish.