Geometric series have the next term equal to the previous term times a constant
Term 2 = Term 1 x n = 28 x n
Term 3 = Term 2 x n = 28 x n^2
Term 3 is 112
28n^2 = 112
n = -2 or 2 depending on whether x is positive or negative.
The tenth term is 28 x n^9 = 14336 if x is positive or -14336 if x is negative