First find what 15% of 600 is. 600 x .15 = 90. So we know that she could have been of by 90 calories. This could mean she was 90 calories to little or to much. So we add 90 to 600, as well as subtract 90 from 600. 600-90=510 600+90=690.
So your answers are B) 690 and C) 510