Asher and Brent builds a toy car in 2 hours.
Brent and Christopher builds a toy car in 6 hours.
Christopher and Asher builds a toy car in 9 hours.
How long does it take for Asher, Brent and Christopher to build a toy car together?
Fraction of the toy car built by Asher and Brent in 1 hour = ¹₂ 
Fraction of the toy car built by Brent and Christopher in 1 hour = ¹₆ 
Fraction of the toy car built by Christopher and Asher in 1 hour = ¹₉ 

Total fraction of the toy car built by Asher and Brent and Christopher in 1 hour
= (¹₂ + ¹₆ + ¹₉) ÷ 2
= (⁹₁₈ + ³₁₈ + ²₁₈) ÷ 2
= ¹⁴₁₈ ÷ 2
= ⁷₉ x ¹₂
= ⁷₁₈ 

Time taken for Asher, Brent and Christopher to build a toy car together
= 1 ÷ ⁷₁₈
= 1 x ¹⁸₇
= 2⁴₇ h

Answer(s): 2⁴₇ h or 2⁴₇ hours