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It can be easily solved mentally.
For a moment, take away these two extra inches.
Then you will have three pieces of x, 2x and 6x inches with the total of 29-2 = 27 inches.
So, x + 2x + 6x = 27,
9x = 27
x = 27/9 = 3.
Thus, in the modified problem, the pieces are 3 inches, 6 inches and 18 inches.
Now return two inches to the 18 inches piece to get the true value of 18+2 = 20 inches.
So, your answer is 3 in, 6 in and 20 in.
This entire reasoning can be done in the head in 30 seconds without paper writing.
Develop your mental skills this way. This problem fits very well for it.
Solved.