College Algebra, Chapter 1, 1.1, Section 1.1, Problem 98

Suppose that a toy maker finds that it costs $c = 450 + 3.75x$ dollars to manufacture $x$ toy trucks. If the budget allows $3600 in costs, how many trucks can be made?

Let $x$ be the number of toy trucks and $c$ is the cost to manufacture toy trucks.
If the budget allows $3600, then
$c = \$3600$

So,

$\begin{equation} \begin{aligned} c &= 450 + 3.75x \\ \\ 3600 &= 450 + 3.75x && \text{Substitute value of } c\\ \\ 3600-450 &= 450 +3.75x -450 && \text{Subtract both sides by 450}\\ \\ \frac{3150}{3.75} &= \frac{\cancel{3.75}x}{\cancel{3.75}} && \text{Divide both sides by 3.75}\\ \\ x&= 840 \end{aligned} \end{equation}$


840 toy trucks can be manufacture in the allowed budget.