CREATE TABLE table_28157 ("Graphics" TEXT, "Launch" FLOAT, "Market" TEXT, "CPU" TEXT, "Code name" TEXT, "Device ID" FLOAT, "Core clock  (  MHz  ) " TEXT, "Execution units" FLOAT, "Shader model" TEXT, "DirectX" TEXT, "OpenGL" TEXT, "OpenCL" TEXT, "Memory bandwidth  (  GB/s  ) " TEXT, "DVMT  (  MB  ) " FLOAT, "CVT HD" TEXT, "QSV" TEXT)

What core clocks ( mhz ) have a 21.3 memory bandwidth ( gb/s )?
SELECT "Core clock ( MHz )" FROM table_28157 WHERE "Memory bandwidth ( GB/s )" = '21.3'
SELECT "Core clock ( MHz )" FROM "table_28157" WHERE "Memory bandwidth ( GB/s )" = '21.3'