Find the value of each variable, line l is tangent.

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°