Simple linear regression is a model that assesses the relationship between a dependent variable and an independent variable. 

The simple linear model is expressed using the following equation: 

Y = β0+ β1X i+ εi

Xi Is independent Yi is dependent.

Example : Between Advertisement and sales . Here when Advertisement cost is high then the sales rate and sales revenue is growing very much.

Here the independent variable (Ads) and dependent variable (sales) are both quantitative.