River C is 200 miles longer than River D. If the sum of their lengths is 5,570 miles, what is the length of each river?
C + D = 5570
C = D + 200
D + C = 5570
D + (D + 200) = 5570
2D + 200 = 5570
2D = 5570 – 200
2D = 5370
D = 2685
C = 2685 + 200
C = 2885
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