What is the number of $6$ digit positive integers whose sum of the digits is at least $52$? 
What is the number of $6$ digit positive integers whose sum of the digits is at least $52$?

My kind of approach was:
I thought to use Multinomial Theorem concept here.
So my primary  aim was to find the coefficient of $x^{52}$in {followed by $x^{53}$ and $x^{54}$[$54$ will be highest because $6\cdot 9=54$]}
$$(x^{1}+x^{2}+x^{3}+\ldots+x^{9})^{6};$$
$=\text{finding coefficient  of }  x^{52 }  \text{ from }  x^{6}\cdot (1-x^{9})^{6}\cdot (1-x)^{-6}$
$=\text{this is equivalent to finding coefficient of } x^{46 } \text{ from }  (1-x^{9})^{6}\cdot (1-x)^{-6}$
$=(1-x^{9}+x^{18}-x^{27}+x^{36}-x^{45})\cdot (1-x)^{-6}$[rest term will be a waste]
This leads to:
$\binom{51}{46}-\binom{42}{37}+\binom{33}{28}-\binom{24}{19}+\binom{15}{10}-\binom{6}{1}$
But it is a wrong answer.  How to use Multinomial correctly?

You should have:
$$[x^{52}](1+x+x^2+\cdots +x^9)^6=[x^{52}]\left(\frac{1-x^{10}}{1-x}\right)^6=\\
[x^{52}](1-x^{10})^6\cdot (1-x)^{-6}=\\
[x^{52}]\sum_{i=0}^6 {6\choose i}(-x^{10})^i\cdot \sum_{j=0}^{\infty}{-6\choose j}(-x)^j=\\
[x^{52}]\sum_{i=0}^6 {6\choose i}(-x^{10})^i\cdot \sum_{j=0}^{\infty}{6+j-1\choose j}x^j=\\
\small{57\choose 52}-{6\choose 1}{47\choose 42}+{6\choose 2}{37\choose 32}-{6\choose 3}{27\choose 22}+{6\choose 4}{17\choose 12}-{6\choose 5}{7\choose 2}=21$$
Wolfram answer.
Indeed, to have the sum of $52$, the digits should be $799999$ or $889999$:
$${6\choose 1}+\frac{6!}{2!4!}=21.$$
