Yellow + dark green + white = 5 + 6 + 1 = 12
Yellow + pink + green = 5 + 4 + 3 = 12
In fact, the fourth one in your list, Rukmini, is the same as Laura's and the fifth and seventh are the same, I think. Do you agree?
After that I did not need to check as the same things would be repeated.
That is we would get a train like green + brown + white which is the same
as brown + white + green.
The train yellow + dark green + white was 12 long and did not use the same
colours as Laura, but was just as long.
Rob's train could have been:
6 + 1 + 2 +3 = 12 : dark green + white + red + green or
5 + 1 + 2 + 4 = 12: yellow + white + red + pink
Charlene's train had the 4 shortest rods: 1 + 2 + 3 +4 = 10. Orange rod is
of the same length, 10.
Ben's train was 7 + 7 + 3 = 17 long.
He might have made:
pink + yellow + dark green + red = 4 + 5 + 6 + 2 = 17
green + brown + pink + red = 3 + 8 + 4 + 2 = 17
green + black + yellow + red = 3 + 7 + 5 + 2 = 17