How can the state trace transactions as to collect tax on transactions made with Zcash? If the state cannot trace the transactions and this becomes black econom

How can the state trace transactions as to collect tax on transactions made with Zcash? If the state cannot trace the transactions and this becomes black economy 2.0 then will it not face banning and seizure from the authorities? Ie how can we build roads and schools in a Zcash economy?