Dice combinations I

This task is about identifying which number combinations are possible.
 
Sam had three dice. When he threw the dice he added the three numbers on the top together. 
For example, if he threw the dice below, the score would be 1 + 4 + 3 = 8.

 
a)
Circle which four of the total scores below are possible when the three dice are thrown.
 
2               7               12               17               18               22
 
b)
Sam threw the three dice twice.
What is the highest total score possible from the six throws combined? __________
 
c) What is the lowest score possible when the three dice are thrown? __________