Marla walks @ 3mph to the store & drives the rest of the way. The distance to the store is 4 miles.
Let Marla walked for t hrs.
From the laws of motion, assuming her walking speed to be uniform,
Distance travelled=speed * time
`rArr t=4/3` , i.e. `1.333` hrs.
Hence, Marla walked for 1.333 hrs.