For the buses travelling in the opposite direction, the slopes of
the dotted lines must be negative. It takes t - 4 minutes for
one of these buses to go the same distance the walker travels in 12
minutes.
represents the speed of the buses going in the same direction to the
speed of the walker.
represents
the speed of the buses going in the opposite direction to the speed
of the walker.
Solution
Solving
the equation
for t results in t = 6. The buses leave the terminals
every 6 minutes.