Question 71109
80*120=9600 SQ FT IS HIS ORIGINAL AREA
THUS 2*9600=19200 WHEN HE DOUBLES IT
THUS (80+2X)(120+2X=19200
9600+240X+160X+4X^2=19200
4X^2+400X+9600-19200=0
4X^2+400X-9600=0
X^2+100X-2400=0
(X-20)(X+120)=0
X-20=0
X=20 ANSWER FOR THE INCREASE WIDTH ON ALL FOUR SIDES TO DOUBLE HIS AREA.
PROOF
(80+2*20)(120+2*20)=19200
(80+40)(120+40)=19200
120*160=19200
19200=19200