least common multiple 105 the prime divisors of 105 , 3,5,7 so our two numbers is multiples of this three numbers just

greatest common divisors 5 so say our numbers a,b

5 is a divisors of a,b , 3,7 in one of them not both say "a" same for "7"

so the cases for a,b

a= 5*3 = 15

b= 5*7 = 35

a+b = 50

a=5*3*7=105

b=5 =5

a+b = 110

so D) is the answer