Question 6261
A) a)add 2 each time to get the next number
   b)subract 3 each time to get the next number

B) a)tn = a + (n - 1)d
in your case:
a = 3 ("a" means first number)
d = 2 ("d" means common difference)

So your formula becomes: tn = 3 + (n - 1)(2)
simplify: tn = 3 + 2n - 2
collect liketerms: tn = 2n + 1 <==answer

to test the answer: try the fifth number, which is suppose to be 11:
t5 = 2(5) + 1 = 11

B) b)try yourself (hint: a = 20; d = -3)