Chapter 1.3, Problem 38E

$\stackrel{\leftrightarrow }{AB}$ and $\stackrel{\leftrightarrow }{EF}$ are said to be skew lines because they neither intersect nor are parallel. How many planes are determined by

a) parallel lines $AB$ and $DC$?

b) intersecting lines $AB$ and $BC$?

c) skew lines $AB$ and $EF$?

d) lines $AB$, $BC$, and $DC$?

e) points A, B, and F?

f) points A, C, and H?

g) points A, C, F, and H?

Exercises $38-40$