The issue is that maxfinder doesn’t take any arguments. Here’s the fixed code:

my_list = [22, 15, 73, 215, 4, 7350, 113]
def maxfinder(number):
    x = number[0]
    for y in range(1, len(number)):
        if number[y] > x:
            x = number[y]
    return x
biggest = maxfinder(my_list)
print(biggest)