Answer:
12/5 days
Step-by-step explanation:
if d=number of days
w=work completed
person one completes w=d/6 (ie. after 6 days (when d=6) work will be completed (w=1))
person two completes w=d/4 (ie. after 4 days (when d=4) work will be completed (w=1))
so total work competed together w=d/6 + d/4
the job is complete when w=1 so
1 = d/6 + d/4
12 = 2d + 3d
12 = 5d
d = 12/5