Relationship between demand and price

Relationship between demand and price, as effect of rainfall manure water on per hectare
productivity of wheat. On the basis of above examples explain the difference between simple correlation and multiple correlation.

Simple Correlation When the relationship between only two variables is studied, it is called simple correlation.
For example., relationship between price and demand or relationship between money supply and price level.
Multiple Correlation When the relationship among three or more than three variables is studied
simultaneously, it is called multiple correlation.
For example, effects of rainfall, manure, water, etc on per hectare productivity of wheat are simultaneously studied.