In the middle school of the 19998 baseball season, Mark McGwire seemed to be on track to break the record for the students most runs batted in. After 40 games, MccGwire had 45 battled n. After 86 games, he had 87 runs batted. Write a linear equation to estimate the number of runs battled in for any given number of games that season.

You have two points:

(40,45) and (86,87)
The slope of the line between those two points is 42/46 = 21/23
So, the equation of the line is
y-45 = 21/23 (x-40)
So, given x games, y is the estimated number of RBIs