Answer: B
In the cis-1,4 isomer with tert-butyl equatorial, Cl must be axial, and axial hydrogens on C-2 and C-6 are anti to it, so E2 is fast. In the trans isomer Cl is equatorial in the locked chair and has no anti hydrogen. The ratio is 3.0×10−3/4.0×10−6=750, so ΔΔG‡=RTln750=8.314×298×6.620=1.64×104 J mol−1=16.4 kJ mol−1 (using log10 by mistake gives 7.1).