Question 908281
27 is not random
4.5*6=27

1/a+1/b=1/x
1/4.5+1/6=1/x
6/27.0+4.5/27.0=1/x
10.5/27.0=1/x
x=27.0/10.5
x=2.57142857 hours working together
check
x/a+x/b=1
x/4.5+x/6=1
2.57142857/4.5+2.57142857/6=1
0.57142857+0.42857143=1
1.0=1
ok