Answer 1

Here's what is happening on the last line
((5 + 10) + (5 + 10))
I think the easiest way to understand it is to replace the function's variable names with the names you're giving it as input
add(add(5, 10), add(5, 10))
I think you want do_twice to look like this
def do_twice(func, x, y):
return func(x, y) + func(x, y)
You could also have the return be return 2 * func(x, y)