By what percentage will the area of a rectangle with sides 8 and 12 cm increase if the sides are increased by 10%?

In the wording of the condition for this task, it is reported that this rectangle has sides with a length of eight and twelve cm.

Then its area is 8 * 12 = 96 cm ^ 2.

If each side of it is increased by 10%, then the smaller side of the resulting 4-gon will be 8 + (10/100) * 8 = 8 + 8/10 = 8 + 0.8 = 8.8 cm, and the large side of the resulting 4-gon will be 12 + (10/100) * 12 = 12 + 12/10 = 12 + 1.2 = 13.2 cm, and its area will be 8.8 * 13.2 = 116.16 cm ^ 2.

Therefore, the area of the original rectangle will increase by 100 * (116.16 – 96) / 96 = 100 * 20.16 / 96 = 2016/96 = 21%.

Answer: 21%.