A completed work in 100 days before and A is 6 times faster than B..

let total days to work is n.

A=6B;

A=(n-100) days taken to complete the work;

where as B=n days ;

A=(B-100)

therefore B=A+100;

A=6(A+100);

A=6A+600;

-600=6A-A

-600=5A

A=-600/5

A=300

B=400;