Cheryl got a bad grade on her test, which she attributes to the fact that she had to work overtime throughout the week and so could not study as much as usual. Cheryl's co-worker also got a bad grade on a test, which Cheryl attributes to her co-worker's laziness. This type of thinking is an example of:

Attribution effect or the fundamental attribution error

Explanation:

Attribution Effect:

In social psychology, attribution effect, also referred as fundamental attribution error explains the tendency for people to under-emphasize the influence of the external factors for the observed behavior of a person like situational explanations of others behavior while over-emphasizing on the internal, based on personality and dispositional explanations instead.

This is a self serving bias. Thus Cheryl attributes her bad grade to the situation while that of her co-worker on the personality trait of her.