Answer :

Nany
5 times 15 equals 75 #multiply
We can do canonical distribution of 75 to see it.
75|3
25|5
  5|5
  1
So, factors of 75 are 3, 5, 5. 
It means that if we multiply 3 *5*5 we will get 75. But we can mulply only 2  (3 and 5 for example) and then mulitply by the third factor, so we have few posibility
3*5*5=75
15*5=75
3*25=75