Table: gm_brand_info
Columns: brand
year_founded
year_began_making_autos
year_joined_gm
markets_served_today

Question: What is the average year to begin making autos for a brand that joined GM in 1917?
SQL: SELECT AVG("year_began_making_autos") FROM gm_brand_info WHERE "year_joined_gm" = 1917