The table shows the mass and melting point of some substances. Melting Point of Substances
Mass
(kg) Melting Point of Tin
(°C) Melting Point of Lead
(°C)
1 W Y
2 232 327

Part 1: What will be the values of W and Y for 1 kg of each substance?
Part 2: Explain your answer for Part 1.

Astudy by solloch and et. al., in 2017, gives the map above which shows the frequency of alleles with a ccr5-delta32 mutations over 87 different countries. this mutation deletes the presence of a co-receptor (ccr5) on the outside of human t-cells (lymphocytes). some viruses, such as the one responsible for the black death and human immunodeficiency virus (hiv), require this receptor for attachment to host cells during the infection process. the black death was an epidemic that passed over northern europe during the 14th century killing nearly 60% of europeans. according to this information, which explanation best explains why northern europeans show a greater immunity for hiv than some other parts of the world?