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Similarities and differences

The print-X-axis function is constructed in more or less the same fashion as the print-Y-axis function except that it has two lines: the line of tic marks and the numbers. We will write a separate function to print each line and then combine them within the print-X-axis function.

This is a three step process:

1. Write a function to print the X axis tic marks, print-X-axis-tic-line.
2. Write a function to print the X numbers, print-X-axis-numbered-line.
3. Write a function to print both lines, the print-X-axis function, using print-X-axis-tic-line and print-X-axis-numbered-line.