user: Question: What is the name of call sign that uses a Frequency MHz of 91.1 FM?
Columns: ['Call sign', 'Frequency MHz', 'City of license', 'ERP W', 'Class', 'FCC info']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['K216FW', '91.1 FM', 'Steamboat Springs, Colorado', 10.0, 'D', 'FCC']
SQL:

assistant: SELECT "Call sign" FROM "Table" WHERE "Frequency MHz" = '91.1 FM';