5+[90+(20-135:ax3)-54]x6=251
[90+(20-135:ax3)-54]x6=251-5
[90+(20-135:ax3)-54]x6=246
90+(20-135:ax3)-54=246:6
90+(20-135:ax3)-54=41
90+(20-135:ax3) = 41+54
90+(20-135:ax3) = 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