CHEMICAL EQUILIBRIUM HELP!!!!?

a mixture of 5.25g I2 and 2.15g Br2, is brought to equilibrium in a 3.15L reaction vessel at 115degreesC. at equilibrium, 1.98g of I2 is present. What is Kc at 115degreesC for the reaction I2(g) + Br2(g) = 2IBr(g)