Refer to the diagram shown below.
The triangles ΔABC and ΔADE are similar because of AAA.
Therefore
[tex] \frac{AC}{AE} = \frac{BC}{DE} \\\\
\frac{x}{x+3.1} = \frac{2.4}{4.2} = 0.5714 \\\\ x = 0.5714(x+3.1)[/tex]
0.4286x = 1.7713
x = 4.133 m
The length of the slide is x + 3.1 = 4.133 + 3.1 = 7.233 m
Answer: 7.2 m (nearest tenth)