The amount after 7 years is given by:

The answer is: $20,948.15
 
        
        
        
-21x+31 this is the answer you were looking for
        
             
        
        
        
The sum of two numbers and their difference is 30.
 
        
             
        
        
        
The slope m of a line
through points 

 and 

  is given by :<span>

Thus, the slope of the line passing through points </span><span>(−1, 7) and (2, 10) is 
</span>

<span>
The equation of a line with slope m passing through a point P(a, b) is given by 
                                        (y-b)=m(x-a).
We can consider any of the points (-1, 7), or (2, 10). Let's choose (2, 10):
                                        y-10=1(x-2)
                                        y-10=x-2
                                           y-x=-2+10
                                           y-x=8                                       
  Answer: </span><span>C. −x+y=8</span>
 
        
        
        
B. The y-intercept is 0 so it can't be C or D and the slope is 5/1. How I remember this is rise/run. Hope this helps!