Can somebody explain how to do 15? asap! : )

Length=2+3w
Area= Length × Width
56= (2+3w)(w)
56=2w+3w^2
56-56=3w^2+2w-56
0=3w^2+2w-56
CONTINUATION IN THE PICTURE
The width is 4
The length is 14;
2+3w
2+3(4)
2+12
14
I stated in the picture that a length cannot be negative. That doesn't mean -14/3 wouldn't work. You may use it if you want.
HOPE THIS HELPS!!!

B. because the 7 represents "seven times", x represents "a number", 12 represents "plus twelve", and -4 represents "minus four"