Let s = northbound train
Then
2s = southbound train
:
Distance = time * speed
4s + 4(2s) = 600
:
4s + 8s = 600
:
12s = 600
:
s = 600/12
:
s = 50 mph is the northbound train
Then
2(50) = 100 mph is the southbound train
:
:
Check:
4(50) + 4(100) = 600
Answer: 
Step-by-step explanation:
The equation of the line is Slope-intercept form is:

Where "m" is the slope and "b" the y-intercept.
The slopes of perpendicular lines are negative reciprocal.
Then, if the slope of the first line is -3, the slope of the other line must be:

Substitute the point (3,4) into the equation and solve for b:

Then the equation of this line is:
