So you already have one equation for the water and one for iron: q=m x c x delta T
The heat given off by the iron is the same amount of heat absorbed by the water, so set the q (heat) equal to each other.
m x c x delta T = m x c x delta T
(let's say the left side of the equation is for the iron and the right side is for the water)
the final temp. has to be the same for both
delta T = T_final - T_initial
let's call T_final: "y" (just as a variable)
delta T = y - T_inital
so now your equation is:
m x c x (y - T_inital) = m x c x (y - T_inital)
(remember the left side of the equation is for the iron and the right side is for the water)
now just plug in your numbers and solve for "y" because that was the variable chosen to represent final temperature.