Well, since it looks like I did problem 1a for you the other day, I might as well answer this.
THINK about the answers you got for problem 1b. Don't just write down some numbers and expect them to be correct. THINK ABOUT YOUR ANSWER. Does it make sense?
As you write it down, you seem to be implying that the function is increasing as it goes from 6.1, 6.2, 6.3, 6.4. LOOK AT THE PLOT. Is the function actually decreasing? Is it remotely possible that your answer is correct? NO!
Anyway, that is irrelevant, as problem 1b explicitly directed you to use interp1 to solve the problem. Did you do that? NO! So you need to redo that part. Your answers were totally wrong anyway.
A quick look at problem 2 seems to be reasonable.
As for problem 3a, it looks like the 2 point estimate for the slope (i.e., velocity) seems to be correct. But you were out to lunch on the 3 point estimate. A 3 point estimate for the first derivative would be a central difference. So try that one again.
