Answer:
(c) both (a) and (b) are correct
Explanation:
Let take the temperature first 90°F and 30°F
Then the difference between the temperature = 90°F-30°F=60°F
Now the temperature is given as 40°F and 20°F
Then the difference between the temperature = 40°F-20°F=20°F
We can see that 60 is 3 times of 20 so option (a) will be correct
Now as the heat is linearly dependent on the temperature as [tex]Q=mc\Delta T[/tex] so at 60°F it will be 3 time hotter than at 20°F
So option (b) is also correct as option (a) and (b) are given in option (c) so option (c) will be the correct option