Hey Rory, I was in class, and I completely blanked out on our lesson of simplifying algebraic expressions and I also have homework!
Ok, what is the problem?
Step One. Distribute. Well, to start off, don't even pay attention to the -17, and only stick to what is next, and inside the parentheses. Act as though the negative sign on the outside of the parentheses is a negative one. Take the number/variables inside the parentheses and multiply by the negative one on the outside of the parentheses. This should bring you to getting -17-t-t-3.
Step Two: Box the like-terms and circle the variables so you can separate the numbers vs. variables. This helps so you don't get confused throughout. You can rearrange the problem as well if this will help you. This should get you to see that -17and -3 are like-terms and so is -t and -t.
Step three: Solving the like terms. Now, you just have to solve the numbers the boxes with boxes, and the circles with circles. The Boxes would be -17 and -3, and the circles would be -t and -t. So the small equation for the boxes would be -17 -3, that would equal -20. And the circles would be -t-t, that would equal -2t. So the fully simplified equation would be -20-2t.