The first one:
15 - [(3 + 4) * 2] = 1
15 - [(7) * 2]
15 - 14 = 1
The second one:
[(15 * 10) divided by 5] - 5 = 25
15 * 10 = 150
150/5 = 30
30 - 5 = 25
The third one:
18 - [6 + (81 divided by 81)] = 11
81/81 = 1
6 + 1 = 7
18 - 7 = 11
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