What is 21 nines multiplied by 16 nines?

What is 21 nines multiplied by 16 nines?

The result of the calculator——
9999999999999998999990000000000000001

5:2 × 4 × 4:3,7:5 × 16 × 5:21,5:4 × 9:7 × 8:5
As like as two peas, how do I calculate these questions?

2 / 9-7 / 16 × 2 / 9 = 9 / 16 × 2 / 9 = 1 / 8
2 of 5 × 4 × 3 of 4 = 2 of 5 × 3 = 6 of 5
1 / 2 × 15 / 1 + 1 / 3 × 2 / 1 = 1 / 2 × 5 / 2 = 1 / 5
4 / 5 × 9 / 7 × 8 / 5 = 7 / 9 × 8 / 4 = 7 / 18
5 / 6 × 5 / 9 + 5 / 9 × 1 / 6 = 5 / 9 × 1 = 5 / 9
5 of 7 × 16 × 21 of 5 = 16 × 3 = 48

How many hours is twelve minutes?

12 △ 60 = 0.2 hours

4.4 hours equals hours and minutes

4.4 hours equals 4 hours 24 minutes