A finished product R is assembled from two units of S and two units of Q. Production of S requires two units of K, three units of L, and one unit of M. Q is produced from two units of X and three units of Z.

1. Construct a product structure tree for R.

2. Assuming zero inventories on hand, how many Zs are needed to produce 90 units of R?

3. If the finished product R takes 2 weeks to assemble, the subassemblies S and Q take 3 weeks, and the components K, L, M, X, and Z take 1 week, when should the order for Z be released if 90 units of R are required by week 8?