Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_6143 ( "Call sign" text, "Frequency" text, "City of license" text, "Watts" real, "Class" text )

### Question ###
How many Watts has a Class of a, and a Frequency of 91.5 fm, and a City of license of elkhart, kansas?

### Accurate SQL ###

SELECT MIN("Watts") FROM table_6143 WHERE "Class" = 'a' AND "Frequency" = '91.5 fm' AND "City of license" = 'elkhart, kansas'