AQA A level chemistry Kp question

Hey guys i'm stuck on this question Hydrogen and iodine react together and the following equilibrium is established: H2(g) I2(g) == 2HI(g)The value of Kp for this equilibrium is 64. In an experiment, equal amounts of hydrogen and iodine were mixed together, and the equilibrium mixture of the three gases at a constant pressure of 100 kPa was found to contain 1.5 moles of iodine. Calculate the partial pressure of hydrogen iodide in the mixture at 723K I know that 64=p(HI)^2/p(h2)*p(I2)I know both the formulas usually needed to work out KP which are mole fraction= number of moles/total number of gas moles. partial pressure of gas = mole fraction*total pressure of the mixture.