Question 909914
1/a+1/b=1/x
1/6+1/9=1/x
9/54+6/54=1/x
15/54=1/x
x=54/15
x=3.6 hours working together
check
x/a+x/b=1
x/6+x/9=1
3.6/6+3.6/9=1
0.6+0.4=1
1.0=1
ok