1.
a=281;
s = a div 100 = 281 div 100 = 2
d = (a - s*100) div 10 = (281 - 2*100) div 10 = 81 div 10 = 8
e = a - s*100 - d*10 = 281 - 2*100 - 8*10 = 1
b = e*100 + d*10 + s = 1*100 + 8*10 + 2 = 182
r := a - b = 281 - 182 = 99
2.
а = 6*12 + 3 = 72 + 3 = 75
b = (a div 10)+ 5 = (75 div 10) + 5 = 7+5 = 12
a = (b mod 10)+ 1 = (12 mod 10) + 1 = 2 + 1 = 3
с = a + b 3 + 12 = 15