The Following Galvanic Cell Has a Measured Cell Potential E°cell

The following galvanic cell has a measured cell potential E°cell = 0.646 V. Pt(s) ∣ Sn⁴⁺(aq) , Sn²⁺(aq) || Ag⁺(aq) ∣ Ag(s) Given that the standard reduction potential for the reduction of Ag⁺ to Ag(s) is +0.800 V, what is the standard reduction potential for the Sn⁴⁺/Sn²⁺ half-reaction?

A) +0.154 V
B) -0.154 V
C) +1.45 V
D) -1.45 V
E) +0.308 V