TeX source:

\begin{aligned} \dfrac{\Delta y}{\Delta x} &=\dfrac{y_{2}-y_{1}}{x_{2}-x_{1}} \\ &=\dfrac{\$ 2.41-\$ 2.84}{2009-2007} \\ &=\dfrac{-\$ 0.43}{2 \text { years }} \\ &=-\$ 0.22 \text { per year } \end{aligned}