Use the Following Table, Showing the Total Output Produced with Various

Use the following table, showing the total output produced with various levels labor and each of two levels of capital to answer the questions.
Units of Capitel
$\begin{array}{l}\text { Units of }\\\begin{array}{ccc}\text { Labor } & \mathrm{K}=2 & \mathrm{~K}=4 \\\hline 1 & 20 & 40 \\2 & 50 & 100 \\3 & 70 & 140 \\4 & 80 & 160\end{array}\end{array}$
-When capital is fixed at 4 units.
a. AP decreases after ______ units of labor. MP decreases after ______ units of labor.
b. At L = 2, AP = ______ and MP = ______.
c. At L = 3, AP = ______ and MP = ______.
d. At L = 4, AP = ______ and MP = ______.