CREATE TABLE table_54316 ("PRR Class" TEXT, "Builderpars_m_singles Model" TEXT, "Build date" TEXT, "Total produced" FLOAT, "Wheel arrangement" TEXT, "Service" TEXT, "Power output" TEXT)

How many total units were built of Model ds-4-4-660 with a b-b wheel arrangement and a PRR Class of bs6?
SELECT SUM("Total produced") FROM table_54316 WHERE "Wheel arrangement" = 'b-b' AND "PRR Class" = 'bs6' AND "Builder\u2019s Model" = 'ds-4-4-660'
SELECT SUM("Total produced") FROM "table_54316" WHERE "Builder\u2019s Model" = 'ds-4-4-660' AND "PRR Class" = 'bs6' AND "Wheel arrangement" = 'b-b'