Expressions and Equations

1. "Five more than a number $n$" means we add $5$ to $n$:

$n + 5$

2. Substitute $x = 4$ into the expression:

$3(4) + 7 = 12 + 7 = 19$

The value is $19$.

3. Subtract $12$ from both sides:

$x + 12 - 12 = 29 - 12$

$x = 17$

Check: $17 + 12 = 29$. Correct.

4. Divide both sides by $5$:

$\frac{5x}{5} = \frac{45}{5}$

$x = 9$

Check: $5 \times 9 = 45$. Correct.

5. The cost of $3$ copies is $3d$. Adding shipping gives:

$3d + 4$

When $d = 9$:

$3(9) + 4 = 27 + 4 = 31$

The total cost is \31$.