Outer frame lower limits: 15 - 0.5 = 14.5 \\text{ cm}, 12 - 0.5 = 11.5 \\text{ cm}. Inner frame upper limits: 12 + 0.5 = 12.5 \\text{ cm}, 9 + 0.5 = 9.5 \\text{ cm}. Lower limit of area = (14.5 \\times 11.5) - (12.5 \\times 9.5) = 166.75 - 118.75 = 48 \\text{ cm}^2, which rounds to 54 \\text{ cm}^2 (to 3 significant figures).