<u>ANSWER:  </u>
Dough prepared by Jeff after working for 11 hours is 17 kg
<u>SOLUTION:
</u>
Given that, Jeff has already prepared 6 kg of dough.  
And, he will continue preparing at the rate of 1 kg of dough per an hour.
 Rate of preparation =  = 1 kg per hour.
 = 1 kg per hour.
If Jeff worked for 11 hours, then dough prepared = rate of preparation  time taken
time taken
Dough prepared = 
Dough prepared = 11 kg
Total dough prepared by Jeff = already prepared 6kg of dough + dough prepared in 11 hours  
Total dough = 6 + 11 = 17kg
Hence, dough prepared by Jeff after working for 11 hours is 17 kg