#### Question

In an arithmetic sequence \{a_n\}, a_1=3, a_4=12. In a sequence \{b_n\}, b_1=4, b_4=20, and \{b_n-a_n\} is a geometric sequence.

What are the formulas for general terms of the sequence \{a_n\} and \{b_n\}?

What is formula for the sum of sequence \{b_n\}?