First you need to distribute the (4x - y) to the other numbers. So we'll distribute it one by one, to make it easier. So taking the 4x from (4x - y), you need to distribute it to (4x + y). So 4x × 4x is 16^2. That's the first part, now we need to distribute the 4x to the positive y, which is 4xy. Now we work on the negative y from (4x - y). Distribute the -y to (4x + y). So -y × 4x = -4xy, and -y × y = -y^2. So now you should have the numbers, 16x^2 + 4xy - 4xy - y^2. The positive 4xy and negative 4xy cancel out so that would just be 0, so you can take that out. Now you should have 16^2 - y^2, and that's the simplified expression.
