In order to find the three possibilities, you must first think of common factors between 30 and 12:
Factors of 30: 1, 2, 3, 5, 6, 10, 15, 30
Factors of 12: 1, 2, 3, 4, 6, 12
We can find three common factors between the two numbers: 2, 3, and 6. So these are three widths that we can use. The length can be found by factoring out the numbers from 30+12x (we can't factor out x):
30+12x=2(15+6x) Width: 2 Length: 15+6x
20+12x=3(10+4x) Width: 3 Length: 10+4x
20+12x=6(5+2x) Width: 6 Length: 5+2x
