It doesn't look like an OCR A Q, but if it were, the Q would state that the specific heat capacity of an aqueous solution is 4.18 J g-1 K-1. And, since the Ca(OH)2 becomes part of the solution, you should include the mass of the solid. You would therefore have to work out the mass of the Ca(OH)2, which considering you know the formula (and hence Mr) and the amount, wouldn't be too much effort.
If the solid did not dissolve and was in excess, OCR A would expect you to not include the mass of the solid in Q=mcDT. Even if some of the solid reacted and became part of the solution. There are plenty more issues with how OCR A does/did it, but my dinner in nearly ready.