The rectangle that has area 400 has width 10, so its length is 40.
A = LW; L = A/W = 400/10 = 40
The length is 10 + 0.2 = 10.2. The width is 10 + 2 = 12
The multiplication is 10.2 * 12
40.2 * 12 = 40 * 10 + 0.2 * 10 + 40 * 2 + 0.2 * 2
40.2 * 12 = 400 + 2 + 80 + 0.4
40.2 * 12 = 482.4