user: Question: What's the average Year with an Issue Price (Proof) of $49.95, and Artist of W.H.J. Blakemore?
Columns: ['Year', 'Artist', 'Mintage (Proof)', 'Issue Price (Proof)', 'Mintage (BU)[ clarification needed ]', 'Issue Price (BU)[ clarification needed ]']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [2000.0, 'D.F. Warkentin', '121,575', '$29.95', '62,975', '$19.95']
SQL:

assistant: SELECT AVG("Year") FROM "Table" WHERE "Issue Price (Proof)" = '$49.95' AND "Artist" = 'W.H.J. Blakemore';