Help i dont understand


heres my code:
m = 5
n = 13
def add_functions(m, n):
a = m+n
return a

print add_function(m, n)

and here's what it keeps returning:
Oops, try again. add_function(9, -13) returned None, did you remember to return the result?


Spelling error.

def add_function(m,n):
    return m + n

print add_function(9, -13)    # -4


thank you so much it helped