What is the ratio of m to n?

(1) If m is decreased by 3 the ratio of m to n becomes 3 :10.
(2) If m + n is increased by 3 the ratio of m to n becomes 7 to 12.

OA is e...however my question is specifically regarding statement 2.

apparently you can translate that statement as

(m + 2)/(n + 1) = 7/12 or (m +1)/(n + 2) = 7/12

how is that? could someone explain how those algebraic translations are derived?