Hey there!! 
Given equation : 
17g - 2g
Let;s first look at something which is common in both the terms. 
Yes, the alphabet which is common is the ' g '. 
Now, let's apply distributive property. 
... 17g - 2g 
... g ( 17 - 2 ) 
Hence, the appropriate answer would be ' D '. 
Hope my answer helps!