Average weight of three friends Amar, Raman and Daman is 70 kg. Another person Vishal joins the group and now the average is 66 kg. If another person Tahir whose weight is 6 kg more than Vishal, joins the group replacing Amar, then average weight of Raman, Daman, Vishal and Tahir becomes 75 kg. What is the weight of Amar (in kg)?

Amar, Raman, Daman average 70 kg means total = 210 kg. With Vishal, average 66 kg for 4 people means total = 264 kg, so Vishal = 54 kg. Tahir = Vishal + 6 = 60 kg. New group (Raman, Daman, Vishal, Tahir) average 75 kg means total = 300 kg. So Raman + Daman + 54 + 60 = 300, giving Raman + Daman = 186 kg. From original: Amar + 186 = 210, so Amar = 24 kg.