In the second line, one cat and two cat heads are equal to 20, and it is known that one cat is 10, so two cat heads are equal to 10 and one cat head is equal to 5.

In the third line, a cat's head and two cat's claws are equal to 9. It is known that a cat's head is equal to 5, then two cats' claws are equal to 4, and then a cat's claws are 2.

So, the last line is 5+2+ 10 = 17.