Answer:
52m
Step-by-step explanation:
as this is a right angled triangle (has a 90° angle), you can use the Pythagoras theorem to work out the missing side.
Pythagoras theorem:

side A squared (labeled on diagram below)
+ side B squared
= side C squared
for this example though, we don't know the length of side B so we need to swap around the formula.

replace the letters for their numbers,
(calculate)
2704 = b² but we want b by itself so we will square root b² (2704)

∴ side B = 52m (remember we were calculating in meters)
I hope this was helpful :-)