Răspuns: a = 27
Explicație pas cu pas:
5+[90+(20-135:a×3)-54]×6=251
[90+(20-135:a×3)-54]×6 = 251 - 5
[90+(20-135:a×3)-54]×6=246
90+(20-135:a×3)-54=246:6
90+(20-135:a×3)-54=41
90+(20-135:a×3)=41+54
90+(20-135:a×3)=95
20-135:a×3=95-90
20-135:a×3 =5
135:a×3 = 20-5
135:a×3=15
135:a=15:3
135 : a = 5
a = 135 : 5
a = 27 → numărul aflat prin metoda mersului invers
