What is the reason for the fourth and eight steps in the proof?

  so the transitive property can be invoked in step 9

Step-by-step explanation:

Without the figure, it is difficult to tell what these steps do. However, the symmetry of the proof suggests that step 4 can match step 8, and its Reason can be "deduced from steps 2 and 3."

The idea of steps 4 and 8, taken together, is to show that DC and DB are both equal to DA, so the transitive property can be invoked in step 9.

i'm pretty sure it's 477,585,296, but perhaps my math is incorrect.

the answer would be 150 books

step-by-step explanation:

if you divide 300 by 2 you will get 150