The Big Bear Lumber Company Is Trying to Decide Whether

The Big Bear Lumber Company is trying to decide whether to sell or process further rough-sawn lumber.The joint cost of producing the rough-sawn lumber is $10,500.The following data are available:
$$\begin{array} { | c | c | c | c | c | } \hline \begin{array}{c}\text { Lumber } \\\text { Type }\end{array} & \text { Number of Boards } & \text { Selling Price per Board }&& \begin{array}{c}\text { Incremental } \\\text { Cost to Process } \\\text { Further }\end{array} \\\hline &&\text { At Split-Off } & \begin{array}{c}\text { After } \\\text { Additional } \\\text { Processing }\end{array} \\\hline \text { A } & 2,000 & \$ 8& \$ 12 & \$ 7,000 \\\hline \text { B } & 1,000 & \$ 8 & 20 & 6,000 \\\hline \text { C } & 500 & 16 & 30 & 1,000 \\\hline\end{array}$$
a. What is the incremental effect, increase or (decrease), on operating income of processing the lumber further?
b. Which type of lumber should be processed further?