How many more followers in percentage are there for the repository used by solution ID 18 than solution ID19?
followers refers to Forks; percentage = divide(SUBTRACT(Forks(Solution.ID = 18), Forks(Solution.ID = 19)), Forks(Solution.ID = 19))*100%
SELECT CAST((SUM(CASE WHEN T2.Id = 18 THEN T1.Forks ELSE 0 END) - SUM(CASE WHEN T2.Id = 19 THEN T1.Forks ELSE 0 END)) AS REAL) * 100 / SUM(CASE WHEN T2.Id = 19 THEN T1.Forks ELSE 0 END) FROM Repo AS T1 INNER JOIN Solution AS T2 ON T1.Id = T2.RepoId