[tex]\bf \begin{array}{llll} _nC_r=\cfrac{n!}{r!(n-r)!} \end{array}\qquad \begin{array}{llll} _{10}C_4\implies \cfrac{10!}{4!(10-4)!}\implies \cfrac{10\cdot 9\cdot 8\cdot 7\cdot 6\cdot 5\cdot 4!}{4!6!} \\\\\\ \cfrac{10\cdot 9\cdot 8\cdot 7\cdot 6\cdot 5}{6!}\implies \cfrac{10\cdot 9\cdot 8\cdot 7\cdot 6\cdot 5}{6\cdot 5\cdot 4\cdot 3\cdot 2\cdot 1}\implies 210 \end{array}[/tex]
that said, check your calculator for a button of [ ₙCᵣ ], and you can use that as well.
