Question

The fixed price of renting a stage is $\$80$ for the first 6 hours, and $\$4$ is charged as an additional maintainance amount per hour. Find the total amount charged for renting the stage for 10 hours.

• A. $80
• B. $100
• C. $120
• D. $140

Answer 1

The correct option is C $120

Consider the points (0, 80) and (20, 160) on the graph

You know,
$\text{slope = unit rate}=\frac{y_2-y_1}{x_2-x_1}$

So, by putting the values you get,

$\text{Slope =}\frac{\$160-\$80}{20-0}$

= $\frac{\$80}{20}$

= $\$4$

You know, equation of a straight line, $y=mx+c$

Also, amount charged when the extra hours were zero will be equal to the y-intercept (c).
From the graph, value of y-intercept (c) = $\$80$.

So, the amount required for 10 extra hours will be
$y=4x+c$

$\Rightarrow y=\$4\times 10+\$80$

$\Rightarrow y=\$120$

∴ Amount charged for 10 extra hours will be $120.