its quite simple really, the sum of the outer line whatever you call it like a circle is 360 degrees a triangle is 180 right? so if the side lines are equevulent that means that the two inner side degrees are equivulent as well, so
180-40=140 but the answer cant just be 140 because there are two corners so now you are going to have to divide it in half to get an even number wich is 70 so there for x=70
