Hi there! :)
Answer:
The length of River C is: 2,900 miles
The length of River D is: 2,600 miles
Explanation:
River C = X + 300 miles
River D = X miles
River C + River D = 5,500 miles
The equation → (X + 300) + X = 5,500
First off, you'll need to solve the equation by isolating "X" in order to find the length of the river D:
(X + 300) + X = 5,500
X + 300 + X = 5,500
Subtract 300 from each side of the equation → 5,500 - 300 = 5,200
X + X = 5,200
Add similar terms together → X + X = 2X
2X = 5,200
Divide each side of the equation by 2 → 5,200 ÷ 2 = 2,600
X = 2,600 miles ⇒ Length of River D
Since River D's length is 2,600 miles and that River C's length is 300 miles longer than River D's, you need to add 300 to the length of River D to find the length of River C:
2,600 + 300 = Length of River C
2,900 = Length of River C
River C + River D = 5,500
2,900 + 2,600 = 5,500 ⇒ YES
There you go! I really hope this helped, if there's anything just let me know! :)