 
 <translate> If they spent two more weeks on their second research expedition than they spent on the first week, they spent 2 + 3 = 5 weeks on the island. In the two expeditions, they stayed on the island for a total of 5 + 3 = 8 weeks. On their third expedition, they spent twice as many weeks as they spent on the second week on the island, which is 2 * 5 = 10 weeks. In all three expeditions, they stayed on the island for 10 + 8 = 18 weeks. Since a week has seven days, they spent 18 * 7 = 126 days on the island.
The answer: 126. <hau> Idan sun yi makonni biyu a tafiyarsu ta biyu fiye da na farkon, sun yi makonni 2 + 3 = 5 a tsibirin. A cikin tafiye-tafiye biyu, sun zauna a tsibirin tsawon makonni 5 + 3 = 8. A tafiyarsu ta uku, sun yi makonni biyu kamar yadda suka yi a mako na biyu a tsibirin, wanda yake 2 * 5 = makonni 10. A duka tafiye tafiye uku, sun zauna a tsibirin na makonni 10 + 8 = 18. Tun da mako yana da kwanaki bakwai, sun yi kwanaki 18 * 7 = 126 a tsibirin. Amsar ita ce: 126. 