Question 100706
D+P=850 D=850-P
300D+225P=217,500 
NOW REPLACE D WITH(850-P) & SOLVE FOR D
300(850-P)+225P=217,500
255,000-300P+225P=217,500
-75P=217,500-255,000
-75P=-37,500
P=-500/-75
P=500 NUMBER OF PONDEROSA PINES SOLD.
850-500=350 DOUGLAS FIRS.
PROOF
300*350+225*500=217,500
105,000+112,500=217,500
127,500=217,500