Explanation:
5.
A B and D C are parallel lines.
"slope" means inclination. and as you can imagine, parallel lines must have the same inclination, or they would not be parallel.
so, the slope of D C must be also 2/7.
4.
same thing as with 5.
both lines are parallel and must therefore have the same slope.
so, the slope of D C is also 3/4. and the first answer is correct.