Answer:
20 HOURS
Step-by-step explanation:
Both the gardener and the helper take 4 hours which means that working together they complete 1/4 of the job.
The gardener alone takes 5 hours meaning that he completes 1/5 of the job in 1 hour.
then, to get the portion done by the helper in 1 hour we subtract fraction done by the gardener in 1hr from the fraction done by both in the same time.
1/4-1/5=1/20
to get the time the helper takes we find the reciprocal of 1/20 which is 20 HOURS
