The Idea I have is to solve this is:

(no. of solution for w + x + y + z = 12) + (no. of solution for w + x + y + z = 13) + (no. of solution for w + x + y + z = 14)

= 15C3 + 16C3 + 17C3

= 1695

is it correct?

(no. of solution for w + x + y + z = 12) + (no. of solution for w + x + y + z = 13) + (no. of solution for w + x + y + z = 14)

= 15C3 + 16C3 + 17C3

= 1695

is it correct?