a) ab + ba0 = 403
10a + b + 100b + 10a + 0 = 403
20a + 101b = 403
2ab - ba = 218
200 + 10a + b - 10b - a = 218
200 + 9a - 9b = 218
9a - 9b = 218 - 200
9a - 9b = 18
9 * (a-b) = 18
a - b = 18 : 9
a - b = 2 => a = b + 2
20a + 101b = 403
20 * (b + 2) + 101b = 403
20b + 40 + 101b = 403
121b = 403 - 40
121b = 363
b = 363 : 3
b = 3
a = b + 2 = 3 + 2 = 5
b) 3ab - ba = 273
300 + 10a + b - 10b - a = 273
300 + 9a - 9b = 273
9a - 9b = 273 - 300
9 * (a-b) = -27
a - b = -27 : 9
a - b = -3 => a = -3 + b = b - 3
ab - ba0 = -99
10a + b - 100b - 10a - 0 = -99
-99b = -99
b = -99 : -99
b = 1
a = 1 - 3 = -2
