Table:
text: 1951 Swiss Grand Prix
Entries
Entries
No_ Driver Entrant Constructor_ Chassis Engine Tyre_
16 Peter Whitehead Scuderia Ferrari Ferrari Ferrari 125 Ferrari 125 F1 1.5 V12s D
18 Luigi Villoresi Scuderia Ferrari Ferrari Ferrari 375 Ferrari Type 375 4.5 V12 P
20 Alberto Ascari Scuderia Ferrari Ferrari Ferrari 375 Ferrari Type 375 4.5 V12 P
22 Nino Farina Alfa Romeo SpA Alfa Romeo Alfa Romeo 159A Alfa Romeo 1.5 L8s P
24 Juan Manuel Fangio Alfa Romeo SpA Alfa Romeo Alfa Romeo 159A Alfa Romeo 1.5 L8s P
26 Toulo de Graffenried Alfa Romeo SpA Alfa Romeo Alfa Romeo 159A Alfa Romeo 1.5 L8s P
28 Consalvo Sanesi Alfa Romeo SpA Alfa Romeo Alfa Romeo 159 Alfa Romeo 1.5 L8s P

text: 1951 Swiss Grand Prix
Entries
Entries
No_ Driver Entrant Constructor_ Chassis Engine Tyre_
30 Louis Chiron Enrico Platé Maserati Maserati 4CLT-48 Maserati 4 CL 1.5 L4s P
32 Harry Schell Enrico Platé Maserati Maserati 4CLT-48 Maserati 4 CL 1.5 L4s P
38 Rudi Fischer Ecurie Espadon Ferrari Ferrari 212 Ferrari Type 375 4.5 V12 P
40 Guy Mairesse Yves Giraud-Cabantous Talbot-Lago Talbot-Lago T26C Talbot 23CV 4.5 L6 D
42 José Froilán González José Froilán González Talbot-Lago Talbot-Lago T26C-GS Talbot 23CV 4.5 L6 D
44 Piero Taruffi Scuderia Ferrari Ferrari Ferrari 375 Ferrari Type 375 4.5 V12 P
46 Francis Rochat Francis Rochat Simca-Gordini Simca-Gordini T11 Simca-Gordini 15C 1.5 L4s E
48 Maurice Trintignant Equipe Gordini Simca-Gordini Simca-Gordini T15 Simca-Gordini 15C 1.5 L4s E

Question: How many drivers were there at the 1951 Swiss Grand Prix with a Ferrari chassis?