You can use a proportion to determine how many hours Seth worked.
If Seth takes 9 hours to make 63 kg of dough, then a fraction can be made: 63/9
How long did Seth take if he made 77 kg of dough? Make another fraction but this time you don't know the hours, so replace that with x : x/77
Now set the two fractions equal to each other : 63/9 = x/77
Solve for x.
Check your answer with mine:
x= 11 hours