TeX source:

\begin{equation} \begin{aligned} \text { Budget } &=\mathrm{P}_{1} \times \mathrm{Q}_{1}+\mathrm{P}_{2} \times \mathrm{Q}_{2} \\ \$ 10 \text { budget } &=\$ 2 \text { per burger } \times \text { quantity of burgers }+\$ 0.50 \text { per bus ticket } \times \text { quantity of bus tickets } \\ \$ 10 &=\$ 2 \times \mathrm{Q}_{\text {burgers }}+\$ 0.50 \times \mathrm{Q}_{\text {bus tickets }} \end{aligned} \end{equation}