The area of an isosceles triangle is ½bh where h is the altitude or height of the triangle.
The height of the triangle is the perpendicular from the apex to the base, which bisects the base as well as bisecting the apex angle.
If area=360cm2 then ½bh=360, 40h=360, h=360/40=9cm, because b=80cm.
Using Pythagoras we can find the length L of the equal sides:
L2=(½b)2+h2=402+92=1600+81=1681=412.
So L=41cm and the perimeter=2L+b=82+80=162cm.