Problem 1: "Imagine that the polynomial $(1 + x - y)^3$ is converted to the standard form. What is the sum of its coefficients?"
Problem 2 (continued): "What is the sum of the coefficients of the terms not containing $y$?"
Problem 3 (continued): "What is the sum of the coefficients of the terms containing $x$?"
I'm able to solve problem 1 & 2, but I've been stuck on 3 for hours..I'd really appreciate it if someone could explain how to solve it :D