I'm brand new to the SolidWorks world and I'm learning on my own. I've done the first few tutorials and I've been following some videos but I figured it would be good for me to do exercise problems. I came across a website called PracticalStudent.com which has four different difficulties of exercises. I'm on the easy section and I've been able to do every single problem except for the 3rd and 8th which are very similar. Attached below is the problem that I have been working on. I can make the general shape but I can't seem to extrude cut the sides so that they will join together at an angle. I've gotten really close I think by making a reference plane along the joint of the two walls but when I try to use the extrude cut tool and give it a direction it gets all messed up. I also included the eighth problem below too which is Capture1.jpg.
Can anyone help me? I feel like I shouldn't be using the extrude cut tool because it looks like you can't adjust the end of the extrude cut just the face that it starts from.