7. A mural is to be painted on a wall that is $15 \mathrm{~m}$ long and $12 \mathrm{~m}$ high. A border of uniform width is to surround the mural. If the mural is to cover $75 \%$ of the area of the wall, how wide must the border be, to the nearest tenth of a meter?

Step 1 ：Let the width of the border be x meters. Then the dimensions of the mural will be \((15 - 2x)\) meters in length and \((12 - 2x)\) meters in height.

Step 2 ：The area of the wall is \(15 \times 12\) square meters, and the area of the mural is 75% of the total area, which is \(0.75 \times (15 \times 12)\) square meters.

Step 3 ：The area of the mural can also be represented as \((15 - 2x) \times (12 - 2x)\) square meters.

Step 4 ：Set up an equation to represent the relationship between the area of the mural and the width of the border: \(0.75 \times (15 \times 12) = (15 - 2x) \times (12 - 2x)\).

Step 5 ：Solve for x: \(x \approx 0.89\) meters.

Step 6 ：\(\boxed{0.9}\) meters is the width of the border, to the nearest tenth of a meter.