For 13: 8 + 30/(2+4). Bidmas means the 30 divided by 6 will occur before the 8 is added. So it is done as 8 plus 30 divided by 6, which is 8 plus 5, giving 13.
For 23: (8+30) /2 +4. Againm bidmas means the /2 will occur before the +4 so what happens is 38 divided by 2 to give 29, then add 4 to get 23.
