The standard potentials are $E^\circ(\text{Co}^{2+}/\text{Co}) = -0.28\ \text{V}$ and $E^\circ(\text{Ag}^+/\text{Ag}) = +0.80\ \text{V}$. What is the standard emf of the cell $\text{Co}(s) \mid \text{Co}^{2+}(aq) \parallel \text{Ag}^+(aq) \mid \text{Ag}(s)$?