Is it true that any marking on an angle means that the angle measure 90 degrees?

In a heat engine if 1000 j of heat enters the system and the piston does 500j of work, what is the final internal energy of the system if the inital energy was 2000 j1.write the equation2.list out your known variables 3. plug the numbers into the equations4.solve 5.write your solution statement that includes initial energy and final energy added.