Answer & Step by Step Explanation:
What the question does not say, but what I will assume is true to have your answer of 10, is that the dimensions must be whole numbers. 
Otherwise there would be an infinite number of cases 
 
So we need 3 multipliers (LWH) to get 28 
the factors of 28 in triples are 
1 1 28 
1 2 14 
1 4 7 
2 2 7 
 
now each one of these can be turned to have a different base 
 
e.g. the first one can be arranged only 2 ways, that is , a base of 1 or a base of 28 
Same is true of last one, but the 2nd and 3rd can each have 3 different bases 
 
so: 
factors-- number of ways 
 
1 1 28 -- 2 
1 2 14 -- 3 
1 4 7 --- 3 
2 2 7 --- 2 
 
total number of ways = 2+3+3+2 = 10 
 
I hope this makes sense to you