<PRE><B>Question 513652</B>
Let x be the number of systems sold = Quantity
Let y be the selling price = Price

 x       y
70     1200
75     1100

Step 1:
Finding the slope, m = {{{(Y1-Y)/(X1-X)}}}
 = {{{(1100-1200)/(75-70)}}}
 = -20

Step 2:
Find the equation of the line; y= mx+c
if x=70 and y=1200 then c?

1200 = -20(70)+c
1200 = -1400 + c
1200+1400 = c
    c = 2600
Finally;
The equation is y = -20x+2600
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