DavePhD is right, and I am accepting and up-voting his answer.  But first ... the real key to the conundrum is a little outside the box.  [It is trimethylamine that has a $pK_b$ of 4.2](https://en.m.wikipedia.org/wiki/Trimethylamine).  Apparently some chemists mistook the basicity of TMAH for that of trimethylamine.