Please help me plsss!

number 3 is the sure answer

My sister said its 3

Step-by-step explanation:

x = 10 - 10sqrt(3)/3

Approximately 4.2265 cm

Volume = 1539.6 cm³

Step-by-step explanation:

Let the height be x

V = (20 - 2x)(40 - 2x)x

V = (800 - 80x - 40x + 4x²)x

V = 4x³ - 120x² + 800x

dV/dx= 12x² - 240x + 800 = 0

3x² - 60x + 200 = 0

x = [60 +/- sqrt(60² - 4(3)(200))]/6

x = [30 +/- 10sqrt(3)]/3

x = 10 +/- 10sqrt(3)/3

Approximately,

15.7735 and 4.2265

d²V/dx² = 24x - 240

For max, d²V/dx² < 0

So, x = 4.2265

V = (20 - 2x)(40 - 2x)x

Plug in x = 10 - 10sqrt(3)/3

V = 1539.600718