The width of the frame is added all around the painting, so you must add 2x to the length of the painting and 2x to the width of the painting to find the total length and width including the frame.
painting length: 30
total length: 2x + 30
painting width: 20
total width: 2x + 20
total area = LW
total area = (2x + 30)(2x + 20)
total area = 1200
(2x + 30)(2x + 20) = 1200
(x + 15)(x + 10) = 300
x^2 + 10x + 15x + 150 = 300
x^2 + 25x - 150 = 0
(x - 5)(x + 30) = 0
x - 5 = 0 or x + 30 = 0
x = 5 or x = -30
The width of the frame cannot be a negative number, so we discard the solution x = -30.
