I hope that works? i also tried to solved it and i got the same thing i just checked it and it said i got it right.
21160000
just multiply every number you see but make sure you multiply the numbers inside the parentheses first
S=2(4x+2x)+4x^2=4x^2+12x
4x^2+12x=7
4x^2+12x-7=0
D=12^2-4x4x(-7)=256
X1=(-12-16)/(2x4)=-3.5 impossible
X2=(-12+16)/(2x4)=0.5
A