The area if a rectangle is found using the formula A = l*w. This means two things multiply to make the area. Take the expression and break it down into two factors to find the possibilities.
30+12x factors into 3(10+4x) so l= 3 and w=10+4x
30+12x factors into 6(5+2x) so l=6 and w = 5+2x
30+12x factors into 2(15+6x) so l=2 and w =15+6x
30+12x factors into 1(30+12x) so l=1 and w= 30+12x
