It Has Been Hypothesized That Overall Academic Success for Freshmen

Multiple Choice

It has been hypothesized that overall academic success for freshmen at college as measured by grade point average (GPA) is a function of IQ scores (X₁) , hours spent studying each week (X₂) , and one's high school average (X₃) . Suppose the regression equation is: Y' = -6.9 + 0.055X₁ + 0.107X₂ + 0.0083X₃.
The multiple standard error is 6.313 and R²= 0.826. For which independent variable does a unit change have the least effect on GPA?

A) IQ scores (X₁)
B) hours spent studying each week (X₂)
C) high school average (X₃)