How is a number like 73,000,000,000,000,000 more challenging to write and comprehend than a number like 73?

Because the number is bigger... and takes longer to write and read.

Because the first number is so huge. We can have a fair idea how big 73 is but its  almost impossible to appreciate the magnitude  of that first number. Also its easy to miscount the number of zeros when you are writing it.  

Numbers as big as the first number are best written in scientific form this one would be written as

7.3 * 10^16   - much easier to write this!

answer: the proof is mentioned below.

step-by-step explanation:

since, given:   lines bc = ef

prove:   lines ac > ef

          statements                                           reason

1. bc=ef                                           1. given

2. ac= ab+bc                                 2. because b is the point between the  

                                                            line segment ac

3.   ac > bc                                       3. because if a line segment is equal to

                                                          the sum of two line segments then it is

                                                          always greater then each of these

                                                          individual line segments

4. ac > ef                                         4. by equality property.