The answers are:
the first term: 21
the fourth term: 22
the tenth term: 39
A(n) = 12+(n - 1)(3)
n = 1
A(1) = 12 + (1 - 1)(3) = 12 + 03 = 12 + 0 = 12
n = 4
A(4) = 12 + (4 - 1)(3) = 12 + 33 = 12 + 9 = 21
n = 10
A(10) = 12 + (10 - 1)(3) = 12 + 9*3 = 12 + 27 = 39
