Fitting a number into sheltered accommodation to the east of a very quiet old city (11)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of ‘a’ (the second one) plus PP ( pianissimo , musically ‘very quiet’) plus UR (‘old city’) plus TENANT, an envelope (‘into’) of NA AN (‘a number’ – I do not see any justfication of the transposition) in TENT (‘sheltered accommodation’ ). ‘To the east of’ indicated the order of the particles.