For the substance SO2F2(g), ΔHºf = -858 kJ mol-1 and the S-F bond, 308.0 kJ mol-1

Determine the average S=O bond energy in SO2F2 in units of kJ.

Is my answer right, if so how do I convert this to kJ?
x= S=O bond
-858= 2(308) + 2(x)
-737kJ/mol