Heat gained by 25º C body = Heat lost by 35º C body
Mc c δθ = Mh cδθ
70 x c x (f - 25) = 70 x c x (35 - f)
where f = final temperature
f - 25 = 35 - f (f and 70 cancel out)
2f = 35 + 25 = 60
f = 602 = 30ºC