The HCF of two positive integers is 7.
Which of the following can be the SUM of those two numbers?

The HCF divides both numbers, so it must also divide their sum. Only 42 is a multiple of 7: writing $42=7\times 6$ gives the pair 7 and 35, whose HCF is 7. Since 48, 55 and 60 are not multiples of 7, no pair with HCF 7 can add up to them.