Răspuns :
252 + 147 + a = 400
399 + a = 400
a = 400 - 399
a = 1
_______
543 = a - 138
a = 543 + 138
a = 681
399 + a = 400
a = 400 - 399
a = 1
_______
543 = a - 138
a = 543 + 138
a = 681
A=400-252-147
A=148-147
A=1
Verificare
252+147+1=400
399+1=400
400=400
A=138+543
A=681
A=148-147
A=1
Verificare
252+147+1=400
399+1=400
400=400
A=138+543
A=681