Study the below given chart carefully to answer the question. 

	Temperature
	Durban	Quito	Columbus	Lisbon	Riyadh
January	20°C	15°C	20°C	22°C	35°C
February	21°C	16°C	18°C	20°C	30°C
March	22°C	18°C	16°C	22°C	32°C
April	25°C	20°C	15°C	25°C	36°C
May	28°C	22°C	14°C	18°C	38°C

What is the difference between the average temperature of all cities in May and that of February?