L=7+W
area=30=LW
so subsitute 7+W for length
30=(7+W)(W)
30=W²+7W
minus 30 both sides
0=W²+7W-30
factor
what 2 numbers multiply to get -30 and add to get 7
-3 and 10
0=(W-3)(W+10)
set to zero
0=W-3
3=W
0=W+10
-10=W
false, can't have a negative width
width=3in
L=7+W
L=7+3
L=10
the length is 10in
the width is 3in
