Answer:
19 or 21.
Step-by-step explanation:
I swear.
5 + 5 = 10
10 + 5 = 15
15 + 4 = 19
________________
9 + 9 = 18
18 + 10 = 28
28 - 5 = 23
There are two nines so
23 - 2 = 21
