Create a metric distant conversion program.. in oracle sql

Ask user three questions and collect them with & substitution values

1^st: from where (it could be cm , mt, km , mm)

2^nd: to where: (it could be cm , mt, km , mm)

3^rd: amount

For instance if 1^stand 2^ndentry same send a print message same metric conversion is not possible and stop the program

If for instance, 1^stvariable value is from km then 2^ndvariable is to where cm and 3^rdvariable amount is 1 then result will be 1km = 1000cm

---i have create one but its not complete .

DECLARE

KM NUMBER := 4;

meter NUMBER := 0;

Cem NUMBER := 0;

BEGIN

meter := km * 1000;

Cem := meter * 100;

dbms_output.Put_line('The value of KM NUMBER KM to meters is: ' ||meter);

dbms_output.Put_line('The value of KM NUMBER KM to centimeters is: ' ||cem);

END;

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how to complete this ?i found mine not complete/