10 cm

Step-by-step explanation:

Formula: V = l × w × h; l = length, w = width, h = height

V = l × w × h

4,000 cm³ = 20 cm × ? × 20 cm

l × h = N

20 × 20 = 400

V ÷ 400 = N

4,000 ÷ 400 = 10

Thus, 10 cm is the width of the box.

Hope It's Helpful