Concept:Forming and solving a pair of linear equations from given conditions.Explanation:Let the number of N50 notes be x.Let the number of N20 notes be y.Total notes: x+y=13.Total value: 50x+20y=530.Dividing the value equation by 10 gives 5x+2y=53.Multiply the first equation by 2: 2x+2y=26.Subtract this from 5x+2y=53:(5x+2y)−(2x+2y)=53−263x=27x=9.So, there are 9 N50 notes.Answer:D. 9