How do the expression 4(3+x) and (3+3+3+3)+(x+x+x+x) compare to one another

They are the same: distributing the 4, we have

And multiplying by 4 means exactly to sum four times the same thing:

distance covered by pamela in 9 l of fuel = 99km

let us apply unitary method here.

distance covered by pamela in 1 l of fuel =99/9 =11 km

now let us find distance covered by pamela if she has 12 l of fuel.

distance covered in 12 l = distance covered in 1 l of fuel * 12

we know that distance covered by here in 1 l is 11 km.

so distance covered in 12 l of fuel = 11*12 = 132 km.