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put this solution on YOUR website!850=D+P D=850-P NOW SUBSTITUTE (850-P) FOR D IN THE SECOND EQUATION
217,500=300D+225P
217,500=300(850-P)+225P
217,500=255,000-300P+225P
300P-225P=255,000-217,500
75P=37,500
P=37,500/75
P=500 NUMBER OF PONDEROSA PINES
850-500=350 NUMBER OF DOUGLAS FIRS
PROOF
217,500=300*350+225*500
217,500=105,000+112,500
217,500=217,500