Question 224817
The equation for C is: {{{n!/((n-r)!r!)}}}.
C is used to find the coefficient in a binomial expansion.
Another way to look at this is that the formula finds the coefficient in the Pascal triangle that corresponds to the {{{(x+y)^7}}} row at the third power. Just a faster way than writing out the Pascal triangle all the time.

This one goes like this:
{{{(7*6*5)/(3*2*1)}}}
The 6 and the 3*2 cancel out to give us:
{{{(7*5)/1}}}
Which is 35.