A solar heating panel on a roof is used to heat 40 kg of water initially at 22 degress celsius, using the sun, which absorbs 750 joules per second. What would the temperature of this water be after 1 hour?

Answer 1

They need to tell you:
(1) if water is flowing through, and at what rate
(2) convective heat loss to the air.
(3) radiative heat loss

They probably expect you to assume no flow and neglect the loss terms. This will lead to a high prediction of the temperature rise. This is a poor way to teach physics, in my opinion.

Multiply 750 J/s by 3600 s. That will be the heat added to the water. Divide that by (Mass)x(specific heat) for the temperature rise.