A researcher collected data on the number of hours students studied per week and their corresponding scores on a standardized test. The following table summarizes their findings:
| Hours Studied | Test Score |
|---|---|
| 5 | 70 |
| 10 | 80 |
| 15 | 85 |
| 20 | 95 |
The researcher wants to establish a linear model to represent the relationship between the number of hours studied (x) and the test score (y). Based on the data, what is the equation of the best-fit line in slope-intercept form (i.e., $y = mx + b$) for this model?