I get the same answer as Pete.
I haven't studied all the answers but Guido it's 30.00948 not 30.948, gotta respect those zero's.
I think it's simplest to first pretend that the tape is exactly 30 meters, do all the calculations, then multiply by the "Riegel tape factor" (30.00948/30 = 1.000316).
So, Raw measurement: 304.80815
Temp correction factor 68-42=26 degrees x 0.00000645=0.000168
304.80815 x 0.000168 = 0.051116.
(Subtract because it's cold, the tape contracts) 304.80815 - 0.051116 = 304.757034.
Now multiply by the Riegel tape correction factor:
304.757034 x 1.000316 = 304.853337
(which I would round to 304.853, about as close as you can read a tape-- ok if you like, take another digit, then 304.8533)
Looking at it now I think my steps are essentially the same as Pete's-- I just like to get the temperature correction amount, then wrestle with the question of whether to add or subtract.
Thanks for the challenge, Pete! But can you tell how you got 4.80815 (that's down to a hundredth of a millimeter, did you carry a machinist's vernier out there?)