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
51 Books
I think this is what you're looking for?
2(12+18) is not equivalent to 24+18
First, you would create an equation for this problem.

=

Next, you would cross multiply.
15x = 1,800
Now, you would isolate the x. To do this, you would divide both sides by 15.
x =
120It is a 120% increase. I hope this helps!