How to combine two queries to one in sql?

I have two sql tables , where one is CARD_TRANSACTION and other RD_PASSENGERTYPE,

the queries are here,

select passengertypekey from CARD_TRANSACTION where daykey = 15738 and id = '70750813';

select passengertypedesc from RD_PASSENGERTYPE where passengertypekey=1;

I want to combine both of them and get the passengertypedesc, i will pass the id and daykey to the query. please help

Thank you