A rectangular prism is a cuboid so volume of cuboid is base area x height which is 5x5x12=300
volume of pyramid is 1/3 x base area x height = 5x5x6x1/3=50 thus volume outside pyramid and inside cuboid is 300-50=250
The vector equation of the line through the origin perpendicular to the plane is
.. (x, y, z) = t(2, 3, -1)
so the point of interest will satisfy
.. 2(2t) +3(3t) -(-t) = -3
.. 14t = -3
.. t = -3/14
and its coordinates are (x, y, z) = (-3/7, -9/14, 3/14)
1/2 = 18 cut
Cut= 1/36
So if victor rides for time t+ 1/36
Alex rides for t
D= 18 (t + 1/36) = 24 t
18 t+ 18/36 = 24 t
6 t = 1/2
T = 1/12 hour = 5 minutes
