this is a correlation between mpg and Engine Size

cor.test(mtcars$mpg,mtcars$disp)
## 
##  Pearson's product-moment correlation
## 
## data:  mtcars$mpg and mtcars$disp
## t = -8.7472, df = 30, p-value = 9.38e-10
## alternative hypothesis: true correlation is not equal to 0
## 95 percent confidence interval:
##  -0.9233594 -0.7081376
## sample estimates:
##        cor 
## -0.8475514

the p-value is .0000000000938 <alpha (.05) therefor there is a significant relationship

the correlation is strong and negative the engine size gets bigger, MPG gets lower