Question

16 3/21- 1 5/21

is it 5 2/21?

Answer 1

well, 16 - 1 is certainly not 5

16 3/21 is just short for 16 + 3/21
you can't subtract 5/21 from 3/21, so let's make that
16 3/21 = 15 24/21
Now you have
(15 + 24/21) - (1 + 5/21)
and now, because addition is associative and commutative, that's
= (15-1) + (24/21 - 5/21)
= 14 19/21

Answer 2

It occurs to me that maybe you meant 15 2/21, not 5 2/21
If so, it indicates that you did the 16-1 right, but subtracted the */21 in the wrong direction.
The answer could have been 15 - 2/21
In other words, 14 19/21

Answer 3

No.

Change 16 2/21 to 15 24/21
Now do the subtraction.