560 : (13 - d) + 20 = 100;
560 : (13 - d) = 100 - 20;
560 : (13 - d) = 80;
13 - d = 560 : 80;
13 - d = 7;
d = 13 - 7;
d = 5.
560 : (13 - d) + 20 = 100;
560 : (13 - d) = 100 - 20;
560 : (13 - d) = 80;
13 - d = 560 : 80;
13 - d = 7;
d = 13 - 7;
d = 5.