Question 934756
Let's call the 4th,5th,6th terms: p, q, r


p = 9-2x
q = x-2
r = 2x-1


If we subtract the 4th term from the fifth, we get q - p. That's equal to r - q since we have a common difference


so,


q - p = r - q


q+q = r+p


2q = r+p


2(x-2) = (2x-1)+(9-2x)


2x - 4 = 2x-1 + 9 - 2x


2x - 4 = 8


I'll let you finish up.