ANSWER
She counted the squares instead of using the scale.
EXPLANATION
The slope of a line is calculated using the formula
[tex]m = \frac{rise}{run} [/tex]
This is the same as:
[tex]m = \frac{y_2-y_1}{x_2-x_1} [/tex]
The given straight line passes through:
(4,24) and (16,18).
We plug in the values to obtain,
[tex]m = \frac{18 - 24}{16 - 4} [/tex]
[tex]m = \frac{ - 6}{12} [/tex]
[tex]m = - \frac{ 1}{2} [/tex]
This is the correct expression for the slope.
But Willa mistakenly counted the squares instead of using the scale and had
[tex]m = - \frac{1}{3} [/tex]
Each box on the y-axis is 3 units and each box on the x-axis is 2 units.
The rise is one box along the y-axis which is equal to 3 units the run is 3 boxes which is equal to 6 units.
The line has a negative slope.
Because she just counted the boxes and did use the scale, she got a wrong answer.
