Question 1090644

 A square field is {{{4c}}} meters on each side.(that "c" is probably typo): I guess it is  {{{40}}} meters, because {{{4}}} is to small size of the side if light towers are built every {{{10}}} meters 

 Beginning at one corner, light towers are built every {{{10m}}} on {{{three}}} sides of the field.

the total length of {{{three}}} sides of the field is {{{3*40m=120m}}}

divide total length by {{{10m}}}:

{{{120m/10m=12}}}

so, {{{12}}} towers are needed