Professor G found a correlation between the number of hours spent doing the work in this class and the score in the weekly quiz. He sampled seven students and a regression line of the hours spent studying and quiz scores was plotted. The intercept of this line was 2 and the slope 0.5. One of the sampled student to have attained a score of 6 in the weekly quiz and spent 10 hours doing the work for the week. Calculate the residual for this observation is: