Answer:
19 or 20
Explanation:
well is see
Monday = 12
Tuesday = 12 + 3 = 15
Wednesday = 15 +3 = 18
so the pattern is 3
but now since there is only 14, 13, 19, and 20
we could say she only added 1 or 1 each time
because it said she wanted cookies to stay about 18
1 x 2 = 2
18 + 2 = 20
or
1 + 18
19
sorry if it's wrong