Part A)
As for branch A, notice the following pattern
[tex]\begin{gathered} 20=10\cdot2 \\ 40=10\cdot4=10\cdot2^2 \\ 80=10\cdot8=10\cdot2^3 \\ 160=10\cdot16=10\cdot2^4 \end{gathered}[/tex]
Therefore, the equation that models branch A is
[tex]10\cdot2^n\to\text{ exponential function}[/tex]
Whereas, as for branch B
[tex]\begin{gathered} 20 \\ 24=20+4 \\ 28=20+8=20+2\cdot4 \\ 32=20+12=20+3\cdot4 \\ \Rightarrow20+4n \end{gathered}[/tex]
which is a linear equation.
Thus, the answer to part A is
Branch A is an exponential function; Branch B is a linear equation, option 2.