Answer: 0.384 millimeters.
Explanation:
Step 1: Area of a rectangle can be found by the formula Area = Length × Width.
Step 2: We have the area of the rectangle to be 48 square millimeters and the length of 8 millimeters.
Step 3: Substitute these values into the formula. Area = Length × Width = 48 × 8 = 384 millimeters. 
Step 4: Since the area is given in square millimeters, we will need to divide the result by 1000, to get the width in millimeters. Width = 384 ÷ 1000 = 0.384 millimeters.
Step 5: Thus, the width of the rectangle is 0.384 millimeters.