Hi Tina!
The linear correlation coefficient is frequently abbreviated as r, while the coefficient of determination is abbreviated as r2. As the abbreviations imply, to get from one to the other you simply square your r value.
correlation coefficient = r = 0.515
coefficient of determination = r2 = (0.515)2
r2=0.265225 ≈ 0.27
For the second part of the question, the coefficient of determination tells you how much of the variation in y (dependent variable) can be attributed to x (independent variable). This means that approximately 27% of the variation in your data can be explained by your independent variable.