It will be the maximum amount of acid that can be formed from the boron in the borax, because you have excess HCl. 16.2g
Boric acid may be prepared by reacting borax (sodium tetraborate decahydrate) with a mineral acid, such as hydrochloric acid:
From the equation we see that ONE mole of borax plus two moles of HCl results in FOUR moles of boric acid. The molecular weight of borax from the formula is 381.38 (decahydrate) and that of boric acid is 61.83 g·mol−1. 25g/ 381.38 = 0.0656 mol borax. 0.0656 * 4 = 0.262 moles of boric acid, or 16.2g.