Paul got a box of 12 crayons for his birthday. During the school year he gave 8 crayons to his friends while he lost 21 crayons. How many more crayons did he lose than those he gave to his friends?
Paul got a box of 12 crayons for his birthday. 
During the school year he gave 8 crayons to his friends. 
That means he's left with 4 crayons. 
He then loses 21 crayons. 
That means he's left with a negative 17 crayons. 

So he lost more than those he gave to his friends by 21 crayons.