We have a square, two equilateral triangles and an isosceles triangle. Focus on working out the largest angle in the isosceles triangle. You can do this using the facts that:
-Angles at a point sum
-Angles in an equilateral triangle are all
-Angles in a square are all
Once you've worked out the largest angle in the isosceles triangle, use the facts that the other two angles in the triangle are equal and that all angles in any triangle sum .