Question 1060529

Let d = cost of desktop
and let a = cost of laptop  
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Write down what we know
   a = d - 300   (1)
0.06d + 0.07a = 252  (2)    
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Eq (1) allows us to substitute "d-300" for "a" in (2):
  0.06d + 0.07(d-300) = 252
      0.13d - 21 = 252
         0.13d = 273
                d = 273/0.13 = 2100

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Ans:
Desktop cost was $2100
Laptop cost was therefore $1800
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Check:   2100(0.06) + 1800(0.07) = 126 + 126 = 252  (ok, finance charges add up)