the scatter plot shows the relationship between the number of chapters and the total number of pages for…

Explanation:

Step1: Assume linear - relationship

Since we use the trend line, assume a linear relationship between the number of chapters $y$ and the number of pages $x$. Let the equation of the line be $y = mx + b$. We would need to find the equation of the trend - line from the scatter - plot (usually by using two points on the line). But if we assume a proportional relationship (simplified case when $b = 0$ for a line passing through the origin, which may be a reasonable approximation if the trend starts from near the origin), and we know two points from the general understanding of the relationship. For example, if we assume that when $x_1$ pages correspond to $y_1$ chapters and we want to find $y_2$ for $x_2$ pages, we can use the proportion $\frac{y_1}{x_1}=\frac{y_2}{x_2}$. Let's assume from the scatter - plot (or a general sense of the linear relationship) that if we assume a book with 120 pages has 12 chapters (a made - up example for illustration purposes, as the actual points on the line are not given precisely). Then $\frac{y}{180}=\frac{12}{120}$.

Step2: Solve the proportion

Cross - multiply the proportion $\frac{y}{180}=\frac{12}{120}$: $120y=12\times180$. $y=\frac{12\times180}{120}$. $y = 18$.

Answer:

C. 18 chapters