select client.name 
from client join Package
on client.AccountNumber = Package.Recipient
where package.Weight = 1.5;

select sum(weight) from Package 
where Sender = (
select Recipient from Package where Weight = 1.5
);
SELECT SUM(p.weight) 
FROM Client AS c 
  JOIN Package as P 
  ON c.AccountNumber = p.Sender
WHERE c.Name = "Al Gore's Head";