H-human a-horse
h+a= 72
2h+4a=192
then do h=72-a
substitute that into the second equation
2(72-a)+4a=192
multiple out
144-2a+4a=192
2a=48
a=24
substitute a into the first equation
h+24=72
h=48
humans- 48
horses- 24
I’m pretty sure the answer is B
We must find UNIQUE combinations because choosing a,b,c,d... is the same as d,c,b,a...etc. For this type of problem you use the "n choose k" formula...
n!/(k!(n-k)!), n=total number of choices available, k=number of choices made..
In this case:
20!/(10!(20-10)!)
20!/(10!*10!)
184756
