This is the concept of geometry, we are required to find the values of angle a,b,c,d; Given that the triangles are by line intersecting two parallel lines, therefore we can conclude that both triangles are similar; thus; angle b=40° ⇒alternate angles angle b= angle c=40° ⇒base angles of isosceles triangles are equal; angle d=180-(40+40)=180-80=100° angle a=360-80=240°
