Consider a simple linear regression relating y = exam score (ranging from 0 to 100 points) to x  = amount (in dollars) paid for a tutor for a sample of n=100 college business students who all paid tutors to prepare for the exam.  The results are: estimated slope=2, R2=.30, s=10, and r=.55. What proportion of the sample variation in exam scores can be explained by the model?

30%

2%

10%

55%