introductory stats question

In a large class, there were 237 students who wrote both the midterm and the final exam. The standard deviation of the midterm grades was 15, and that of the final exam was 18. The correlation between the grades on the midterm and the final was 0.63. Based on the least squares regression line fitted to the data of the 237 students, if a student scored 19 points below the mean on the midterm, then how many points below the mean on the final would you predict her final exam grade to be?

What I have come up with so far is the equation 0.63(18)/15=19/x. I know the equation for the slope is the correlation coefficient times the standard deviation of y divided by the standard deviation of x. The question wants to know the final exam grade so that must be the dependent variable(y-axis). Another alternative to the equation(which I think is more correct) is
0.63(18)/15=(mean-19)/(mean-x) but that isn't solvable since there are two variables. Thanks.