http://imgur.com/tboXQ.png

Can anyone help me out with this problem? What does it exactly mean by "left hand slope"?

Here's what I've done:

(6939-6653)/10 = 28.6

(7231-6939)/10 = 29.2

29.2 + 28.6 / 2 = 28.9 so this is the slope of the tangent or am I missing something?