Let $P$ be your money: $$P(1+jt)=3P\qquad\Longrightarrow\qquad 1+jt=3\qquad\Longrightarrow\qquad t=\frac{2}{12\%}=16.\bar6\,\text{years}$$ that is $16$ years and the fractional part $\frac{2}{3}=0.\bar6$ year (i.e. 8 months)
Let $P$ be your money: $$P(1+jt)=3P\qquad\Longrightarrow\qquad 1+jt=3\qquad\Longrightarrow\qquad t=\frac{2}{12\%}=16.\bar6\,\text{years}$$ that is $16$ years and the fractional part $\frac{2}{3}=0.\bar6$ year (i.e. 8 months)