SQU is acute. If you add the angles together (71 + 18) it equals 89, which is just below 90 degrees, which means it is an acute angle. (To help remember that, think of "cute" in the word acute, as in, small and adorable, so smaller than 90 degrees)
RQU is obtuse. If you add the angles together (71 + 18 + 19) it equals 108, which is above 90 degrees, which means it is an obtuse angle. (To help remember that one, think of the word obtuse, it kind of sounds close to obese, which means huge, so the angles is way bigger than 90 degrees)
Hope that helps!