$a)$

$\text{Europa: }19,2\%\cdot 3mld=0,192\cdot 3mld=0,576mld=0,576\cdot 1000000000=576000000$

$\text{Afryka: }9,8\%\cdot 3mld=0,098\cdot 3mld=0,294mld=294000000$

$\text{Australia i Oceania: }0,9\%\cdot 3mld=0,009\cdot 3mld=0,027mld=27000000$