function code snippet that has function calls I have never seen before. How does it work.

[Ronald Cosentino]

def funA(x,y,z):
    return (x+y) * z
def funB(x,y):
    return(x-y)
print(funA(4,funB(2,3), funB(3,2)))

the answer is 3. I don't know how it works.