Answer:
It is 5/5 or 1/1 as it goes up 5 and to the left 5!!!
 
        
             
        
        
        
Rx - sx + y = b
WHEN SOLVING FOR X :
rx - sx + y = b
We must get x onto it's own side, so subtract y from both side.s
rx - sx = b - y
Then, factor out x.
x(r - s) = b - y
Then, divide both sides by (r - s).
x(r - s) ÷ (r - s) = b - y ÷ (r - s)
Simplify.
x = b - y / r - s → 

WHEN SOLVING FOR Y :
rx - sx + y = b
We need to isolate y, so get rid of everything BUT y on the left side.
Subtract rx from both sides.
-sx + y = b - rx
Then, add sx to both sides.
y = b - rx + sx
~Hope I helped!~
 
        
        
        

Y is the total price. X is the number of months. 30 is a flat, one time payment.
 
        
                    
             
        
        
        
You can use any letter but when you label it x you find x