You must first get a common denominator by multiplying (1/3) by 5 and (-2/5) by 3 to get the equation (5/15)+(-10/15)= -5/15 which can be simplified to 1/3.
The copper oxide can then react with the hydrogen gas to form the copper metal and water. When the funnel is removed from the hydrogen stream, the copper was still be warm enough to be oxidized by the air again.
