1. Diego subtract 10 to each length as follows:
15 - 10 = 5
36 - 10 = 26
30 - 10 = 20
18 - 10 = 8
12 - 10 = 2
21 - 10 = 11
In this way only the side which length is 5 is correct
2. Jada scales the drawing by the next scale factor:
5/15 = 1/3
where 5 is the desired length and 15 is the length of the original side.
Then, the other lengths are:
36*1/3 = 12
30*1/3 = 10
18*1/3 = 6
12*1/3 = 4
21*1/3 = 7
3. Diego's procedure is incorrect, as it is seen in his drawing. Subtraction is not the correct way to scale a drawing. On the other hand, Jada's procedure is correct.