The correct answer is - 319 km.
Giza is relatively close to the Mediterranean Sea, and the air distance between it and the Mediterranean Sea is around 319 km. Giza is part of Cairo, and it can not really be considered as a district on its own by Egyptian rules, but still it has an important status because of its historic significance, and the tourist income it gets in the country's budget, so very often it is referred to as a separate unit.