The scheme is given by $$\frac{v_m^{n+1}-v_m^{n-1}}{2k} + b\frac{v_m^{n+1}+v_m^{n-1}-v_{m-1}^n-v_{m+1}^n}{h^2} = 0$$
where $v_m^n$ is the numerical solution at the $m^\text{th}$ spatial coordinate and $n^\text{th}$ time step. It approximates a solution to
$$\frac{\partial u}{\partial t} - b\frac{\partial^2 u}{\partial x^2} = 0$$
I need to find a bound for the local truncation error. Is there a relatively quick way of doing this? I need to do this sort of thing on an exam, and I don't want to take too long, or rush it and make a mistake, possibly taking even longer.