$3.$ Consider the supply chain illustrated below:

Last year, the retailer's weekly variance of demand was $500$ units. The variance of orders was $600,1200,$ and $1150$ units for the retailer, wholesaler, and manufacturer, respectively. $($Note that the variance of orders equals the variance of demand for that firm's supplier.$)$

a$)$ Calculate the bullwhip measure for the retailer. Is the bullwhip effect present here?

b$)$ Calculate the bullwhip measure for the wholesaler. Is the bullwhip effect present here?

c$)$ Calculate the bullwhip measure for the manufacturer. Is the bullwhip effect present here?

d$)$ Which firm appears to be contributing the most to the bullwhip effect in this supply chain? Why?