divide both sides by the $2.06 which gets you 2.56/2.06 = (1+g)4
Then you just take the fourth root of both sides and you're left with 1-g on the right. I'm sure you can isolate for g from there on.
Substitute x = 1+g , and solve it like any other equation involving x.
2.56/2.06 = x4
4sqrt(2.56/2.06) = x
x = 1.055828, however, x = 1+g, so g = x-1, g = 1.055828-1 = 0.055828