FYI, sorry if i'm wrong but it's been a while since I did some of these problems..
Assuming we have a solute that doesn't dissociate ( so i= 1), we have
(change in Temperature) delta T = k m i
where k = 3.51
m = 4 molals
i = 1
so basically your change in temperature is 14 degrees.
And since this colligative property is dealing with boiling point elevation , its 70.4 + 14 = 84.4