Question 86342
Let x=number of Douglas Firs that was bought
Then 850-x=number of Ponderosa Pines that was bought

Cost of the Douglas Firs=$300x
Cost of the Ponderosas=$225(850-x)

Now we are told that the total cost of the trees is $217,500.  So our equation to solve is:

$300x+$225(850-x)=$217,500  divide each term by 25 (reduce size of numbers) 

$12x+$9(850-x)=$8700  ger rid of parens

$12x+$7650-$9x=$8700  subtract $7650 from both sides

$12x+$7650-$7650-$9x=$8700-$7650  collect like terms

$3x=$1050  divide both sides by $3

x=350-------------------------------number of Douglas Fir's that was bought

850-x=850-350=500-----------------number of Ponderosa Pines that was bought

CK

$300(350)+$225(500)=$217,500

$105,000+$112,500=$217,500

$217,500=$217,500

Hope this helps----ptaylor