3 × [3 + 4 × (15 + 5 × m) : 9] = 69
3 + 4 × (15 + 5 × m) : 9 = 69 : 3
3 + 4 × (15 + 5 × m) : 9 = 23
4 × (15 + 5 × m) : 9 = 23 - 3
4 × (15 + 5 × m) : 9 = 20
4 × (15 + 5 × m) = 20 x 9
4 × (15 + 5 × m) = 180
15 + 5 × m = 180 : 4
15 + 5 × m = 45
5 × m = 45 - 15
5 × m = 30
m = 30 : 5
m = 6
