So initial moles are
H2: 2
I2: 2
2HI:0
at equilibrium, this changes to
H2: 2-x
I2: 2-x
2HI: 2x (=0+2xX)
your expression is:
49 = (2x)^2/(2-x)^2 (you don't need concentrations, since the molar ratio of products: reactants is 1:1.
solve this equation? by square rooting both sides and rearranging. hopefully that will get you the right answer for what x is, and then you can substitute that into the initial expressions for moles at equilibrium.