Question 171883
30*20=600 m^2 is the pool area.
(30+2x)(20+2x)=2*600
600+40x+60x+4x^2=1,200
4x^2+100x+600-1,200=0
4x^2+100x-600=0
4(x^2+25x-150)=0
4(x-5)(x+30)=0
x-5=0
x=5 m. for the width of the deck.
Proof:
(30+10)(20+10)=1,200
40*30=1,200
1,200=1,200