I am little doubtful with regard to below points.
The equation I understood is
d1 +d2 + d3+ d4+d5+d6=19
where each 0$\leq$di$\leq$9 (Actually answer comes when I take each di in this range)
my query was why not each di will be in range 1$\leq$di$\leq$9
because question mentions for positive integers so each digit must be from 1 to 9.