What is the point slope form of (4,-1) m= -2

Abby is preparing fruit punch for her party. she starts with a bowl filled with liquid that has 1/2 fruit juice and 1/2 sprite, but she decides it's too fruity. so she pours out 1/4 of the liquid, and then fills the bowl up again with sprite. what fraction of the punch is now sprite?

Just tell me how to set up the equation.

Fast! find the length of cu. the triangles are similar. show your work.