please help solve this problem

indicate quarsecy required for each parent. Assumn lok-for-tot ondering. This exertise contahe only parts b and c. Click the icon to view intormation about the steppen. The product ofructure is as follows: b) Choose the correct time-phased structure. c) Develop a net material requirements pian for F (enter your responses as whole numbers). \begin{tabular}{cccc} \hline Item & \begin{tabular}{c} Lead \\ Time \end{tabular} & \begin{tabular}{c} On-Hand \\ Inventory \end{tabular} & Components \\ \hline Stepper & 2 & 20 & A(2),B(3),C(1) \\ A & 1 & 20 & D(1),F(3) \\ B & 2 & 20 & E(1),F(2) \\ C & 3 & 10 & D(2),E(3) \\ D & 1 & 15 & \\ E & 1 & 5 & \\ F & 2 & 20 & \end{tabular}