What is th unit digit in ( 3 65+6 59+7 71 )?

Unit digit in 3⁴ = 1
∴ Unit digit in ( 3⁴ )¹⁶ = 1
∴ Unit digit in 3⁶⁵ = 3
Unit digit in 6⁵⁹ = 6
Unit digit in 7⁷¹ = 3
∴ Required unit digit = Unit digit in ( 3 x 6 x 3 )
= Unit digit in 54
= 4