let the lengths of the sides of the triangle be: the equal sides 'a', 'a' and the third side 'b'

two equal sides of a triangle are each 5 meters less than twice the third side

a + a = 2b - 5

2a = 2b - 5

the perimeter is 55 meters

a + a + b = 55

2a + b = 55

by solving the system of equations

2a = 2b - 5

2a + b = 55

we find

a = 17.5 m

b = 20 m

the length of the sides are 17.5, 17.5 and 20 meters.