user: Question: What's the sum of population when the membership is 51439 for fewer than 40 branches?
Columns: ['Province', 'Membership', 'Population', '% LDS', 'Branches', 'Total Congregations']
Types: ['text', 'real', 'real', 'text', 'real', 'real']
Sample row: ['Alberta', 78120.0, 3645257.0, '2.14%', 32.0, 208.0]
SQL:

assistant: SELECT SUM("Population") FROM "Table" WHERE "Membership" = 51439.0 AND "Branches" < 40.0;