![\begin{gathered} a)32 \\ b)Plan\: B \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/wqmt25vcxr9l2tvjblojzs8k1tvnisc9co.png)
1) Firstly, let's express each plan by using linear equations.
Plan A:
5x+320
Note that the $320 payment is done once, then 5 per session.
Plan B
15x
2) To get to know when opting for plan A or Plan B is not relevant, we need to equate both equations and solve it for x (x stands for the number of sessions)
![\begin{gathered} 5x+320=15x \\ 5x-15x=-320 \\ -10x=-320 \\ 10x=320 \\ (10x)/(10)=(320)/(10) \\ x=32 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/w6td7pw1c3fwerlhcz3hj8wczagtpsy0wg.png)
So if you attend 32 sessions then, doesn't really matter which plan is it.
3) Now, let's figure out which plan is more interesting to take:
![\begin{gathered} C_A(x)=5x_{}+320 \\ C(1)=5(1)+320 \\ C(1)=325 \\ --- \\ C_B(x)=15x \\ C_B(1)=15(1) \\ C_B(1)=15 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/fsk2rjdyvo92mr56tpgrfkoxnpjh3x0508.png)
So the plan B is cheaper to attend 1 session