I'm learning how to do reactions with the Three Moment Theorem and in the solution for problem 830, it has 1077.27/12 = 538.64.....this clearly isn't correct.

Am I missing something? I tried searching to see if this has been addressed elsewhere, but some guidance would be very helpful and many thanks in advance.

Yes, it is clearly not correct. Thank you for pointing this out. We flag the page for correction and will update it the soonest possible time. Again, thank you.