2. Consider the following two-dimensional convection-diffusion equation: Ou =U- + U at ax ax Obtain an explicit finite difference equation using first-order forward time, first-order forward in space (for the convectionerm), and second-order central spatial differencing (for the diffusion terms). You do not have to derive the difference approximations; simply use them. Remember to include all super- and subscripts, as well as the "order" term including the lowest-order error term for each variable. Combine all order terms at the end of the equation. (12.5 points)