They both are 180 degrees.
One possible difference is that a straight angle is just a single angle measuring 180 degrees, while a linear pair supplementary angle are pairs of adjacent angles that add up to 180 degrees.
Well your answer for problem 4 is 28. IM not sure what the boxes are for though...
The acceleration is defined as the ratio between the change in velocity and the time elapsed to perform such a change.
These "changes" are indicated with the capital greek letter delta,
, and when you write
you mean the difference between the finial and the inital values of the variable x:

So, the acceleration is defined as

In this case, the initial velocity is 35, the final velocity is 65. Assuming we start the clock at the beginning of the observation, the inital time is 0 and the final time is 5. So, we have
m/s^2