Let us begin by extracting the required information
In 1 hour,
[tex]\begin{gathered} Tom\text{ can clean }\frac{1}{x}\text{ }of\text{ the building} \\ Maria\text{ can clean }\frac{1}{x\text{ + 9}}\text{ of the building} \\ Bob\text{ can clean }\frac{1}{2\text{x + 18}}\text{ of the building} \end{gathered}[/tex]We are required the size of the building all three janitors can clean in 1 hour
To calculate this, we add the fractions for each janitor:
[tex]=\text{ }\frac{1}{x}\text{ + }\frac{1}{x\text{ + 9}}+\text{ }\frac{1}{2x\text{ + 18}}[/tex]Simplifying, we have:
[tex]\begin{gathered} \text{= }\frac{(x+9)(2x+18)\text{ + x(2x+18) + x(x+9)}}{x(x\text{ + 9)(2x + 18)}} \\ =\text{ }\frac{2x^2+18x+18x+162+2x^2+18x+x^2\text{ + 9x}}{x(x\text{ + 9)(2x + 18)}} \\ =\frac{5x^2\text{ + 63x + 162}}{x(x\text{ +9)(2x + 18)}} \end{gathered}[/tex]Hence, the fraction of the building they can clean in 1 hour is:
[tex]=\frac{5x^2\text{ + 63x + 162}}{x(x\text{ +9)(2x + 18)}}[/tex]