is the regression line $\hat Y = -0.1 + 0.007X$ where (X) is the sat score and (Y) is the GPA
The coefficient of determination is $0.3 = R^2$.
So based on this data, the regression line and coefficient of determination, can we say that researchers should use SAT (X) scores to estimate GPA (Y). I think no but not sure how to explain it. I think 30% variation is too little
The closest $R^2$ is to $1$, the better the regression is. It also depends on the number of points you have, the more you have, the closer to 1 it should be. However, 0.3 is way too small. A good approximation starts at least at one digit (0.9), maybe (0.99) (considering enough values).