What is the output of this code?

What is the output of this code?

def operate(x, y):
    if isinstance(x, str) and isinstance(y, str):
        return x + y
    elif isinstance(x, int) and isinstance(y, int):
        return x * y
    else:
        return None

print(operate('Hi', 'There'))
print(operate(3, 4))
print(operate('Hi', 4))