9514 1404 393
Answer:
m = 18
Step-by-step explanation:
In an arithmetic progression, the middle term of three is half the sum of the terms on either side.
a1 +a3 = 2(a2)
(m +9) +(2m +7) = 2(2m -1)
3m +16 = 4m -2 . . . . . . collect terms
18 = m . . . . . . . . . . . . . . add 2-3m
