Hello there,
The answer is 11.9m
There could be another way to solve it, but i like to think of it as ratios.
Since both triangles are similar, that means that the second triangle was enlarged with a certain scale factor.
To find that scale factor, we can divide 4.2m/3m which is equal to 1.4m.
Similarly, dividing 14.7m/10.5m gives us 1.4m
Now that we’re sure the scale factor is 1.4m, we can multiply 8.5m by 1.4m to get the corresponding missing side on the similar triangle. The answer is 11.9m.
I hope this helped!