To solve the problem, we first identify the pattern in the given equations:

• (12 + 13 = 25 = 2×12 + 1)
• (13 + 14 = 27 = 2×13 + 1)
• (14 + 15 = 29 = 2×14 + 1)

The pattern for consecutive numbers (a) and (a+1) is:
(a + (a+1) = 2a + 1)

For (19 + 20), (a = 19):
(2×19 + 1 = 38 + 1 = 39)

Answer: 39

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