10 identical balls in 3 boxes. (assuming boxes to be identical because if boxes were distinct then it should have been mentioned)
$\Rightarrow Part(10,1) + Part(10,2) + Part (10,3)$
$Part(10,1) = 1 $
$Part(n,k) = part(n-1,k-1) + part(n-k,k) $
$Part(10,2) = Part (9,1) + Part(8,2)$
$Part(8,2) = Part (8,1) + Part (6,2)$
$ Part(6,2) = Part(6,1) + Part (4,2)$
$ Part(4,2) = Part(4,1) + Part (2,2)$
$ Part(2,2) = Part(2,1) + Part (0,2)$
$ Part(2,2) = 1$
$ Part(4,2) = 2$
$ Part(6,2) = 3$
$ Part(8,2) = 4$
$ Part(10,2) = 5$
similarly after calculation $ Part(10,3) = 8$
$\Rightarrow 1 + 5 +8 = 14$
if boxes are distinct,
$\binom{10+3-1}{3-1} = \binom{12}{2} = 66$