Let Us Suppose We Are Predicting the Score on a Training

Let us suppose we are predicting the score on a training posttest from the number of years of education and the score on an aptitude test given before training. Here is the regression equation: Y = 25 + .5X₁ +10X₂,
Where X₁ = years of education and X₂ = aptitude test score.
What does the .5 in front of X₁ tell us?

A) Where the equation crosses the y-axis
B) How much change in posttest score you get per unit change in aptitude test score
C) How much change in the posttest score you get per unit change in years of education
D) How much change in the years of education you get per unit change in posttest score