you don't need to calculate anything, it's simply an equilibrium question.
The question asks which substrate will dominate. I believe it was G6P -> F6P, dG = +30kJ. At that point, you know that G6P will dominate because the delta-G is positive and thus favors the left (whoops, had right at first, sorry about that) hand side of the equation. The question then asks what the equilibrium constant will be, but you don't have to do any calculations. Remember that equilibrium is equal to products/reactants. The answer choices, IIRC, were 0, 0.5, 1 and 1.5. 0 is a junk answer, no Keq is 0. 1 is perfect equilibrium (eg dG = 0), and 1.5 favors the right. The only answer choice is 0.5, which means that the left side is favored.
F6P/G6P = Keq, G6P > F6P at equilibrium, thus, the answer has to be less than 1.