7. Shown below is a portion of the computer output for a regression analysis relating sales ($y$ in millions of dollars) and advertising expenditure ($x$ in thousands of dollars).(12%)

| Predictor | Coefficient | Standard Error |
| --- | --- | --- |
| Constant | 4.00 | 0.800 |
| x | 0.12 | 0.045 |

ANOVA

| | df | SS |
| --- | --- | --- |
| Regression | 1 | 1400 |
| Error | 18 | 3600 |

a. What has been the sample size for the above regression analysis?