Calculate the concentration of the potium permanganate solution?

1.8g of iron(II) ammonium sulphate, Fe(NH4)2 (SO4)2. 6H2O, was dissolved in 35cm^3 of distilled water. The Solution was then diluted to 50cm^3 using dilute sulphuric acid. The final solution was titrated against potium permanganate solution and 40cm^3 of the potium permanganate Solution was required to reach the end-point at which all the iron(II) had been converted to iron(III). Calculate the concentration of the potium permanganate solution.