Let y be the yield of bushels of wheat in comparison to the amount of rainfall
Let x be the amount of rainfall that occurs (in inches)
If the linear regression equation is y = 47.3 + 0.78x, then per inch of rainfall will yield an addition 0.78 bushels (plugging into x the additional inches of rainfall).
Therefore, on the first inch of rainfall, y = 48.08.
On the second inch of rainfall, y = 48.86.
And so on.