To combine the like terms, add both the numbers with the variable t together and the others without together.
-3.6+1.2= -2.4
-1.9t + 5.1t = 3.2t
Putting the sums together you should get:
-2.4 + 3.2t
If you're confused about how to subtract/add negative numbers, I like to ignore the sign--depending on what it is of course. For example, I rewrite -3.6+1.2 as 3.6-1.2. When you get the answer for that (2.4), add a negative symbol in front because the negative number was greater than the positive. I hope that helps rather than confusing you.
