[derez]

Here is conceptual code, not debugged:
sub combination(x,y)
a = 1
for i = 1 to x
a = a*i
next
b = 1
for i = 1 to y
b=b*i
next
c=1
for i = 1 to x-y
c= c*i
next
return a/(b*c)
end sub