A television poll of 151 persons found that 68 watched ""Law and Disorder""; 61 watched ""25""; 52 watched ""The Tenors""; 16 watched both ""Law and Disorder"" and ""25""; 25 watched both ""Law and Disorder"" and ""The Tenors""; 19 watched both ""25 "" and ""The Tenors""; and 26 watched none of these shows. How many persons watched all three shows?