If they sold 30 shares for $700 to pay your taxes, then that $700 (or most of it) would also be included in Box 2, Federal Taxes Withheld of Form W-2 (some portion may be in Boxes 4 and 6 for your SS and Medicare Tax).
This is a "sell to cover" exercise, where you sell only
enough shares to cover the option costs, fees (fees, if any) and applicable taxes. The proceeds of the 30 shares are reported as income (Box 1 of W-2) and applied to taxes withheld and option costs/fees (if any).
