I was too just a couple of weeks ago. So direct variation is the constant way to variables change together. EX: 
x  y
1 2
2 4
3 6
Direct variation must be in the format b=ka where k is a constant. So the direct variation here could be y=2x. Understand?
        
             
        
        
        
Let the slower train's velocity be x-21
Let the faster train's velocity be x
We know that the approach speed is the sum of both speeds, so x+x -21= 2x-21.
The approach rate is given by Distance/time = 471/3 = 157mpH
x+x-21=157
2x=157+21
2x=178
x=89mph
The slower train is travelling 89-21 = 68mph
The faster train is travelling 89mph.
 
        
             
        
        
        
Answer:
The slope is 2 
Step-by-step explanation:
Formula: y2-y1/x2-x1= 11-5/7-4 = 6/3=2
 
        
             
        
        
        
The bottle of 100 would be lowest. $8.13 ÷ 100 lozenges = $0.08 per lozenge