:/ sorry im really bad at math haha if you can explain so i can try and understand it !

So they're proportional.
This means that the 2 triangles are exactly the same BUT the right one is smaller than the other, so all measurements are smaller too.
So to find the distance, you need to find the scale factor. 
Think of it like this: 82m becomes 73.8m, and 92m becomes 82.8m.

Find the scale factor by finding the ratio.
73.8/82 = 9/10 or 0.9
You could do the same thing with the other two numbers too (92/82.8), gives the same answer.

Times the ratio by the distance of the bigger triangle:
0.9 x 47 = 42.3m