TeX source:

\begin{align*} B_3 &= 1.08B_2\\ &= 1.08(1.08B_1) \\ &= 1.08(1.08(1.08B_0))\\ &= 1.08(1.08(1.08 \cdot 100)) \\ &= 1.08^3 \cdot 100 = 125.971 \end{align*}