Using sed

Write a one-line sed command that will replace all multiple spaces in a file called names.txt (this is an arbitrary file that you may create yourself) by only one space.

Consider the following file called system.txt:

1 2 3 4

5 6 7 8

9 He 11 Hg

Ts H 15 Be

17 Mc Li 20

Write a one-line sed command that replaces the second number in every line with the string system, without the quotes. For example, after running the appropriate sed command, the following would be output to the terminal:

1 system 3 4

5 system 7 8

9 He system Hg

Ts H 15 Be

17 Mc Li system