Diborane $($B$2$H$6),$ a useful reactant in organic synthesis, may be prepared by the following reaction, which occurs in a nonaqueous solvent:

NaBH$4+$ BF$3->$ B$2$H$6+$ NaBF$4($unbalanced$!)$

If the reaction has a $66\%$ yield of diborane, how many grams of NaBH$4$ are needed to make $31\mathrm{.}8$ g B$2$H$6?$