tolong dong,ini gimana caranya bantu saya terimakasih

1.{a, b}
2
{}, {a}, {b}, {a,b}
2²=4
2.{a, b, c}
3
{}, {a}, {b}, {c}, {a, b}, {a, c}, {b, c}, {a, b, c}
2³=8
3.{a, b, c, d,}
4
{}, {a}, {b}, {c}, {d}, {a, b}, {a, c}, {a, d}, {b, c}, {b, d}, {c, d}, {a, b, c}, {a, b, d}, {a, c, d},{b, c, d}, {a, b, c, d}
2⁴=16
Jd banyaknya himpunan bagian {a, b, c, d,..} =2^n