Find the fourth, sixth, and thirteenth terms of the sequence described by each
explicit formula.
15. a(n) = 6 + (n - )
16. a(n) = 12 + (n - 1)(5)
17. a (n) = -2.2 + (n - )
18. a(n) = 5 + (n - 1)(0.5)
19. a(n) = -3 + (n - 1)6)
20. a(n) = -7.6+ (n 1)(3)