Towards the end of the "The Critical Density" video we discussed how we could determine the flatness of the Universe given observations of a faraway object of known size. From theoretical predictions, we know that the typical distance between spots seen on the faraway cosmic microwave background is xCMB = 100 Mpc, and we know that the distance to the cosmic microwave background surface is DCMB = 13 Gpc. (We will learn much more about these topics in the CMB module.)

What is the maximum allowed angle subtended by the typical distance between spots if the universe is negatively curved? (These distances are technically "comoving distances" but we will not address aspects of distance measures in cosmology in this course.) Give your answer in degrees, showing two decimal places.