Answer:
unsaturated solution of NH4Cl
Step-by-step explanation:
To answer this question, you will need to refer to the solubility curves reference diagram (I have attached this diagram).
The curve shows the temperature on the x-axis and the solute per 100 grams of water on the y-axis.
So, you would simply check the diagram and find the intersection point between a temperature of 40 degrees Celsius and a 42 gram solute per 100 grams of water (the value is expected to be somewhere between 40 and 50 of course)
Doing this, you would find that the closes t solution fitting the required criteria is the unsaturated solution of NH4Cl
Hope this helps :)