I cannot change the angle between two lines

[creatersin]

I’m trying to change the angle between two lines to 45 degrees. I’m watching an education and at the education video the angle between two lines appears and able to change manually. But at mine, angle isn’t able to change manually. Is this because the new version of program has deleted this feature? Orange design is education video and other is mine.

[RevenueMonkey]

I’d draw a floating line Parallel to the grey wall and Disconnect it. Use the Move/Rotate tool, moving the pivot point to the end of the line. Rotate the line by 45°. Click on the 45° and lock it. Then make the line Tangent to the circle and extend the line until it crosses the grey wall. Use the Trim tool to cut of the ends.

[creatersin]

Thank for the solution. Problem solved.