SUBTOTAL X 6% = 5 SUBTOTAL=?
$$\\ST*6\%=5\\ ST=5\div 6\%\\ ST=5\div 0.06\\$$
$${\frac{{\mathtt{5}}}{{\mathtt{0.06}}}} = {\frac{{\mathtt{250}}}{{\mathtt{3}}}} = {\mathtt{83.333\: \!333\: \!333\: \!333\: \!333\: \!3}}$$