Answer:
So in 8 hours he will set 8 more diamonds.
Step-by-step explanation:
Jeweler A can set in 60 minute (1 hour) 60/20=3 diamonds.
Jeweler B can set 60/15=4 diamonds.
Jeweler B sets 1 more diamond than A in one hour.
So in 8 hours he will set 8 more diamonds.