Ernie has three times as many stamps as Peggy, or 3*75=<<3*75=225>>225 stamps.
Bert has 4 times as many stamps as Ernie, or 4*225=<<4*225=900>>900 stamps.
Thus, Peggy would need 900-75=<<900-75=825>>825 more stamps to have a collection as large as Bert's.
#### 825