In the image what part of the earth is experiencing the summer season?

Northern Hemisphere.

Explanation:

The side that is experiencing the summer in the northern hemisphere as the summer solstice takes place n the June 21st as the north pole tilts directly to the sun at the 23.4° on the earth's axis as the sun here is directly over the tropics and thus the closer the earth is to the sun the more will be the impacts of the summer. The summer is thus associated with the hot and dry weather conditions that develop in the months of 1 May to 1 August.  And the growth of a savanna type climate. Characterized by the increase of the daylight of the sun.

A,) cause a & b are equal & both gives 180°