## Algebra: A Combined Approach (4th Edition)

Answer: When x = 1 unit, Surface area = 22 square units. When, x = 3 units, Surface area = $78$ square units. When, x = 5.1 units, Surface area = $154.2$ square units. When, x = 10 units, Surface area = $400$ square units.
Given formula for surface area of box = $2x^{2}+20x$ Thus, for different values of $x$, we should have different surface areas of the box. To find out, we simply substitute the given value of $x$ in $2x^{2}+20x$. Thus, When x = 1 unit, Surface area = $2\times(1)^{2}+20(1)$ = 2+20 = 22 square units. When, x = 3 units, Surface area = $2\times(3)^{2}+20(3)$ =$2(9) + 60 = 18+60 = 78$ square units. When, x = 5.1 units, Surface area = $2\times(5.1)^{2}+20(5.1)$ =$2(26.01) + 102 = 52.2+102 = 154.2$ square units. When, x = 10 units, Surface area = $2\times(10)^{2}+20(10)$ =$2(100) + 200 = 200 +200 = 400$ square units.