Aboard a med$-$evac helicopter, one medic throws the other a pen. An observer on the ground measures that the helicopter is traveling horizontally in a straight line at $80$ mph$.$ As the helicopter passes the observer, he measures that the pen$$s velocity appears to be seven$-$eighths of the velocity of the helicopter. At what velocity do the medics measure the pen? $($Assume the positive direction is the direction in which the helicopter is moving.$)$

Select one:

a$.$

$150$ mph

b$.$

$90$ mph

c$.$

$35$ mph

d$.$

$10$ mph