I don't know really ask someone smarter than me
LiftA= u m/s ( upwards)
LiftB= -u m/s(downward)
Velocity A relative to B= V lift A- V lift B=8m/s
u-(-u)=8
u=4m/s
Lift A= 4 m/sec
Lift B= -4m/sec
For someone standing on first floor will be stationary W.r.t to the lift.
V lift A relative to Man= V liftA - V man= 4m/s
V lift B relative to Man= V lift B- V Man= -4 m/s
When substituting, you want to take the y value from one equation and plug it into the y variable in the other equation to find the x value. When you find the c value, you plug the number into one of the equations to get your y value.