The table below shows (lifetime) peptic ulcer rates (per 100 population), U, for various family incomes, x, as reported by the 1989 National Health Interview Survey.
| Income |
4000 |
6000 |
8000 |
12000 |
16000 |
20000 |
30000 |
45000 |
60000 |
| Ulcer rate |
12.9 |
12.8 |
13.3 |
12.6 |
12.9 |
11.8 |
11.5 |
9.5 |
7.9 |
(a) Find the equation of the regression line.
Ulcer rate, U(x) =___
(b) Estimate the peptic ulcer rate for an income level of x0= 21000 according to the linear model in part (a).
Ulcer rate, U(x0)= ___