Eagle and falcon age problem

An eagle is 4 times as old as a falcon. Three years ago, the eagle was 7 times as old as the falcon. 
Find the present age of each bird. 

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x = falcon's age now
4x = eagle's age now   {the eagle is 4 times as old as falcon} 

x - 3 = falcon's age 3 years ago
4x - 3 = eagle's age 3 years ago 

4x – 3 = 7(x – 3)   {three years ago, eagle was 7 times the falcon}
4x – 3 = 7x – 21   {used distributive property}
4x = 7x -18   {added 3 to both sides}
-3x = -18   {subtracted 7x from both sides}
x = 6   {divided both sides by -3}
4x = 24   {substituted 6, in for x, into 4x} 

falcon is 6 now
eagle is 24 now 

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