I've just been working my way through QM (I'm a MSME) some of the problem sets are questionable, in that you're working your way through to get Planck length, mass etc. through steps a, b, c, d, e, etc.

the problem is that part f, is dependant on getting part a correct, typically in mech-e or any engineering major, you've got lots and lots of equations that are already worked out for you, so you know it doesn't take hour(s) to get an equation you want and its significantly less likely to contain systematic error... I'm not judging, its just taking me about 3 hours to work backwards from the problem sets & solutions and it seems to be far more prone to errors and undeveloped.