the cutoff point is irrelevant as it is not asked in the question (and I agree with rabolisk, even if you didn't check by hand to see the graph actually goes through the origin, the computer-given values are so small that they are negligible)
Now for the slope; I did not plot it in a computer program, but can see the line is 100% accurately linear. If you do plot it though, be careful of plotting the x and y values correct (do not mix them up, a common mistake). Then when the computer gives you a value, take the extra minute of time to check if this is a reliable value by checking it by hand. Remember: slope of a graph = dy/dx
then finally check significant numbers