Question 720879
Guidance for question #A:


Pick any point on L1.  Find the line through this point and perpendicular to L1.  The line found this way should be expected to intersect with line L3.  Find this point of intersection, using whatever method you wish, since you'll work this with two simultaneous linear equations.  Substitution, elimination, simple matrix, your choice which.

NOW, use the distance formula to find the distance between these two points.