9 m
Step-by-step explanation:
The formula is a^2+b^2=c^2
If...
a = 12 m
c = 15 m
Then,
a^2+b^2=c^2
144+b^2=225
b^2=225-144
b^2=81
b=9
Length is 9 m.
It has been given that
its width is 12 metres
and its diagonal is 15 metres
So by Pythagoras theorem we
get length to be 13 metres
Hope it helps♥️❤️