The average life expectancy in the United States, $L$, has been rising steadily over the past few decades, as shown in the table below. Let $t$ be the number of years since 1920, (so $t = 0$ represents the year 1920).

(a) Find the equation of the regression line.

Average life expectancy, $L(t)=$ .
Note: this is a function of $t$ (not $x$).

(b) Estimate the average life expectancy in the United States in the year 1952 according to the linear model in part (a).

Average life expectancy in 1952 $\approx$ .