Find the first, fourth, and tenth terms of the arithmetic sequence described by the given rule. a(n) = 12+(n-1)(3)

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 + 0*3 = 12 + 0 = 12

n = 4
A(4) = 12 + (4 - 1)(3) = 12 + 3*3 = 12 + 9 = 21

n = 10
A(10) = 12 + (10 - 1)(3) = 12 + 9*3 = 12 + 27 = 39