calculus please help

Question

Write the sum using sigma notation:

A= __________________ 

B= __________________ 

Answer 1

a_n = 7 + 3(n-1)

49 = 7 + 3(n-1) => n=15

∑a_n = 15*7 +3∑n - 3∑1 =105 + 3∑n - 45 = 60 + ∑n

where the ∑ runs from 1 to n

This is not exactly the form you question requests, but it is correct. However,

A = 15 and B = 7+3(n-1)

Answer 2

The answer is B=3k+4 and A=15.

Answer 3

49 = 7 + 3(n - 1)

15 = n

A = 15

B = 7 + 3(n - 1)