Because 8 x 21 = 168
21
0.381
21 divided in to 3 equal parts = 7
45
22.5
To divide by a fraction, multiply by its reciprocal. In this instance, 16/21 / 8/9 is equal to 16/21 x 9/8 = 0.857142 recurring (that is, 0.857142857142...)
21
8
(-21/4) + (9/8) = -4.125
2.625
0.0016