3x + 2 - 1.7 = 0.6x + 31.4
1.3x + 2 = 0.6x + 31.4
If you subtracted 1.7 from 3x in the first equation above to obtain 1.3x in the second equation, that's wrong.
3x and 1.7 are not like-terms because one of them contains x and the other does not.
However, 2 and -1.7 are like-terms (they're both constants), so you can combine them to get 0.3