How many years since first plans to undertake a major restoration of Mdina's wall were made to it was inaugurated as a public garden?
return the  first plans to undertake a major restoration of Mdina 's wall were made ;return Mdina 's wall was  inaugurated as a public garden ;return year of #1 ;return year of #2 ;return difference of #4 and  #3
['select', 'select', 'project', 'project', 'arithmetic']