Hello!
The exercise doesn't say the final temperature, but we are going to assume that the increase is of 20 °C (The procedure is the same, just change the final temperature) To calculate the heat absorbed by water, we need to use the equation for
Heat Transfer, in the following way (assuming that the heat increase is 20°C):

So, the Heat absorbed by water is
1297,04 J
Have a nice day!
Answer:
Mass of KCL = 218 grams.
Explanation:
Step 1: calculate the heat that must be absorbed(q).
Heat that must be absorbed(q) is calculated as follows:
q= m c (T2-T1).
q = 750g (4.18 J/gC)(20-4 C) = 5.016X10^4 J = 50.16 kJ
Step 2: we determine moles of KCL as follows:
Moles KCl = 50.16 kJ / 17.2 kJ/mol = 2.92 moles.
Step 3: calculate mass of KCL:
Mass of KCl = 2.92 mol X 74.55 g/mol = 218g.
Therefore, 218 grams of KCL would have to be dissolved into 750 g of 20.0°C H2O to produce the solution.