a + b = 245 (timbre)
a - 12 = (b + 12) : 4
4×a - 48 = b + 12
b = 4×a - 60
inlocuim in prima relatie pe b
a + 4×a - 60 = 245
5 × a = 245+60 = 305
a = 305 : 5
a = 61 timbre (in primul plic)
b = 245 - 61 = 184 timbre (in al 2-lea plic)
Verificare:
61 + 184 = 245
61 - 12 = (184+12):4
49 = 196 : 4
49 = 49 (adevarat)