let
x-----------> the first side
y-----------> the second side
z----------> the third side
we know that
x+y+z=747------> equation 1
x=y-45------> equation 2
z=2x-----> equation 3
substitute 3 in 1
x+y+[2x]=747-------> 3x+y=747--------> equation 4
resolve the system of equation 2 and equation 4
x=y-45
3x+y=747
using a graph tool
see the attached figure
the solution is
x=175.5 m
y=220.5 m
z=2x-----> z=2*175.5------> z=351 m
the answer is
x=175.5 m
y=220.5 m
z=351 m
