So you know the answer but dont understand why they are correct? I'll have a go at explaining, hope this helps.
Lets say that your altimeter is reading 2000ft, and the temperture is greater than ISA. Your actual altitude will be greater than 2000ft. If the temeprature was below ISA, then your actual altitude is less than 2000ft. For details on how to calculate the correction you should refer to DAP INTRO 2-2 and 2-3. Note that the table also work in reverse (i.e for hot temps)
So to your first question. 40deg is about ISA +25 and you are 1600ft AGL. Using the table from DAP 2-2 you can enter the graph at an aerodrome temp of -10deg (becasue that is ISA-25, remember it also works in reverse). Go along until you hit the 2000ft line then go down until you reach the AGL line, and then go to the right where you should get a temp correction of about 150ft. For the cold temp scenario you would add this value but for the hot temp scenario you take it off. So your indicated height is 4200 - 150(from the correction graph) which gives you 4020ft. answer (d)
For the next question I couldnt get the answer listed. I suspect the answer is incorrect. However it is the only answer that is higher than 2000ft by about the right amount. I got 2200ft at a stretch. So yeah (b). But note that the method for the questions is basically the same...use the graphs!
Note, I do these calcs everyday for a living and just looking at this again (and punching it into my spreadsheets), I am defintely convinced that the answer given for the second question is inaccurate.
Hope this helps, Alpha
Sorry I might add that there is a rough rule of thumb of 4% of the altitude for every 10deg (+ or -) from ISA. So for question 2 its ISA+20. 8% of 5000ft is 400ft....this gets you much closer to the supplied answer...but its not terribly accurate.