Thank you! You caught a major typo on both the bluffing and calling frequencies. I used the pot size of 10 instead of the bet size of 7.50 for the numerator of both of those fractions. I went back and fixed it.

Here's a quick proof for those who are interested:

Suppose we bluff x percent of the time. We want the EV of our opponent's call to be the same as the EV of our opponent's fold from our opponent's perspective. The EV of folding is 0, so we want the EV of his call to equal that to find the unexploitable bluffing frequency.

(x)(17.50) + (1-x)(-7.50) = 0
17.50x - 7.50 + 7.50x = 0
25x = 7.5
x = 7.5/25
x = 7.5/(7.5+7.5+10)
x = bet/(bet+bet+pot)

Thanks again.