simple trigger ..could anyone fix it for me ?

hi ...
i am new to oracle and PL/SQL ...

i have a problem in a form ...its a non database form which i created using developer 6i ...i have wrote the codes but its not running ... i am not really sure about the codes although its VERY SIMPLE ...

this is the code

begin
if : pay.hours_worked<40 then
: pay.gross=Houres_worked*hourly_rate;
end if;

if : pay.hours_worked>=40 then
: pay.gross=Houres_worked (hourly_rate*1.5);
end if;

if : pay.radio='member' then
: pay.fee= -20;
end if;

if : pay.radio='non' then
: pay.fee= 0;
end if;

if : pay.list='ohio' then
: pay.bonus=50;
else
: pay.bonus=100;
end if;

: pay.net=: pay.gross+: pay.fee+: pay.bonus;

end;

i am sure that the codes for the radio buttons and the list is wrong ... also i dont know what to chenge in the properties of the tools ...i only change that database items into No ...

please could anyone help me with this and tell me what is wrong ...

i have attached the form i created