So the formula you will be needing looks like this:
Q = m * c * (T_f - T_),
where Q is the heat transferred to the water, m is the mass of the water, c is the specific heat capacity of water, and T_f and T_i are your final and initial temperatures, respectively. Now, you know that the final temperature is 100 degrees Celcius, because that is the temperature at which water boils. Rearranging the formula so that it gives you the initial temperature, you get:
T_f - Q/(m*c) = T_i
Putting in the numbers, we get:
T_i = 41.8 degrees Celcius
