1 mole of Br2 reacts with 2 moles of NO to produce 2 moles of NOBr.
Hence, 5.0 moles of Br2 will react with 10.0 moles of NO to produce 10.0 moles of NOBr.
Hence, the sum of the number of moles of NO reacted and the number of moles of NOBr formed is 10+10=20.