Pre-Algebra Examples

 $\begin{array}{r} h = & 7 - 2 x \\ l = & 10 - 2 x \\ w = & x \end{array}$

Step 1

The surface area of a box is equal to the sum of the areas of each side of the box.

$2 \cdot (l e n g t h) \cdot (w i d t h) + 2 \cdot (l e n g t h) \cdot (h e i g h t) + 2 \cdot (w i d t h) \cdot (h e i g h t)$

Step 2

Substitute the values of the length $l = 10 - 2$ , the width $w = x$ , and the height $h = 7 - 2$ into the formula.

$2 \cdot 10 - 2 \cdot x + 2 \cdot 10 - 2 \cdot 7 - 2 + 2 \cdot x \cdot 7 - 2$

Step 3

Simplify each term.

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Step 3.1

Multiply $2$ by $10$ .

$20 - 2 \cdot x + 2 \cdot 10 - 2 \cdot 7 - 2 + 2 \cdot x \cdot 7 - 2$

Step 3.2

Multiply $2$ by $10$ .

$20 - 2 x + 20 - 2 \cdot 7 - 2 + 2 \cdot x \cdot 7 - 2$

Step 3.3

Multiply $- 2$ by $7$ .

$20 - 2 x + 20 - 14 - 2 + 2 \cdot x \cdot 7 - 2$

Step 3.4

Multiply $7$ by $2$ .

$20 - 2 x + 20 - 14 - 2 + 14 x - 2$

Step 4

Simplify by adding terms.

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Step 4.1

Add $20$ and $20$ .

$- 2 x + 40 - 14 - 2 + 14 x - 2$

Step 4.2

Add $- 2 x$ and $14 x$ .

$12 x + 40 - 14 - 2 - 2$

Step 4.3

Simplify by subtracting numbers.

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Step 4.3.1

Subtract $14$ from $40$ .

$12 x + 26 - 2 - 2$

Step 4.3.2

Subtract $2$ from $26$ .

$12 x + 24 - 2$

Step 4.3.3

Subtract $2$ from $24$ .

$12 x + 22$

$12 x + 22 x^{2}$