Problem: Use Riemann Sums to approximate the area under the curve

f(x) = 5x^2 + 1 on [0,2] using left endpoints and n=4

The attached image is my professor's work (this is a study guide for my exam). After finding change in x (y-x)/n or 2-0/4 = 1/2 in this case...I'm pretty much lost. Specifically...where is the prof getting the 3/4 from in f(3/4) on the right side of her work? Does the 1/2 come from the change in x or is that just coincidental?

Thank you very much!