This is just a slight various of a break-even problem. Just set the 2 equations equal to each other.
First equation: TC=8.25x+65054
Second equation: TC=19.50x+12539
19.50x+12539=8.25x+65054
Subtract 8.25x from both sides; also subtract 12539 from both sides; which gets you:
11.25x=52515
Divide both sides by 11.25, to give you the break-even quantity (where both are the same quantity):
x=4,668 units