Question 615661
C stands for the combination formula


In general <img src="http://latex.codecogs.com/png.latex?\LARGE \dpi{120} _{n}C_{r} = \frac{n!}{r!(n-r)!}" title="\LARGE \dpi{120} _{n}C_{r} = \frac{n!}{r!(n-r)!}" />


So in this case, n = 20 and r = 6. So plug them in to get


<img src="http://latex.codecogs.com/png.latex?\LARGE \dpi{120} _{20}C_{6} = \frac{20!}{6!(20-6)!} = 38760" title="\LARGE \dpi{120} _{n}C_{r} = \frac{n!}{r!(n-r)!}" />