200 - {100-2×[58+(30-18 :z)]:4} = 141
100-2×[58+(30-18 :z)]:4 = 200-141
100-2×[58+(30-18 :z)]:4 = 59
2×[58+(30-18 :z)]:4 = 100 - 59
2×[58+(30-18 :z)]:4 = 41
2×[58+(30-18 :z)] = 41 × 4
2×[58+(30-18 :z)] = 164
58+(30-18 :z) = 164 : 2
58+(30-18 :z) = 82
30-18 : z = 82 - 58
30-18 : z = 24
18 : z = 30 - 24
18 : z = 6
z = 18 : 6
z = 3