Let the number of markers be N. Cameron's share is 5N/8 and Peter's 3N/8 making the ratio 5:3. Peter gets 5N/16 from Cameron, which gives him in total 3N/8+5N/16=11N/16. Cameron has 5N/16 markers left. The difference is 30 markers: 11N/16-5N/16=30; 6N/16=30; 3N/8=30, so N=8*30/3=80. Cameron gave 5/16*80=25 markers to Peter.