Comparing two groups

Is this t test here the right test to do?

> g3mpg <- mtcars[mtcars$gear==3,”mpg”]
> g4mpg <- mtcars[mtcars$gear==4,”mpg”]
> t.test(g3mpg,g4mpg)

If the data are not normal, what is the correct test to do?

Use the broom package to create a nice overview of the results of the t-test.
What is the biological effect when you compare the gas usage of cars with 3 and cars with 4 gears?
Answer should be a number rounded up to 1 decimal place. 

Starting from the list of groups that was generated below, what would be the correct code for the t test that compares the gas usage of cars with 3 and cars with 4 gears?

> L <- split(mtcars,mtcars$gear)