Greetings!
This can be solved by creating an algebraic equation:
[tex]8.75(30)+11x=400[/tex]
Solve for x.
[tex]262.5+11x=400[/tex]
Add -262.5 to both sides.
[tex](262.5+11x)+(-262.5)=(400)+(-262.5)[/tex]
[tex]11x=137.5[/tex]
Divide both sides by 11.
[tex](11x)/11=(137.5)/11[/tex]
[tex]x=12.5[/tex]
You must work 12.5 hours as landscaper to earn $400 a month.
Hope this helps.
-Benjamin