(length)(width) = 30
2(length) + 2(width) = 34
Start by finding factor pairs of 30: (1 and 30), (2 and 15), (3 and 10), (5 and 6). Now figure out which of these pairs solve the second equation above.
Logically you could eliminate the first one (because 2 x 30 is greater than 34 alone), so move on to the second.
2(2) + 2(15) = 34
4 + 30 = 34
34 = 34
Therefore the dimensions are 2 x 15