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A farmer grows only pumpkins and corn on her 420 -acre farm. 
This year she wants to plant 250 more acres of corn than pumpkins. 
How many acres of each crop does the farmer need to plant?
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Let P be the pumpkins area (in acres).
Then the corn area is (P+250) acres, according to the condition.
With it, write the total area equation as you read the text
    P + (P+250) = 420  acres.
Simplify and find P
    2P = 420 - 250 = 170
     P             = 170/2 = 85.
ANSWER.  85 acres of pumpkins and 85 + 250 = 335 acres of corn.
CHECK.   The total area is  85 + 335 = 420 acres.    ! Correct !
Solved.
                There is another way to solve the problem.
You can write the system of two equations
    C + P = 420
    C - P = 250.
To solve it, add the equations.
Doing this way to the end, you will get the same answer.
Solved   (in two ways).
Happy learning  (!)