Help with the first maths question pls? I got 3/4.?

a)
Length * Width = Area of the base
(2x + 5) x = 58
2x² + 5x = 58
2x² + 5x - 58 = 0

b)
For equation ax² + bx + c = 0
x = [-b ± √(b² - 4ac)] / (2a)

For equation 2x² + 5x - 58 = 0
x = {-5 ± √[5² - 4*2*(-58)]} / (2*2)
x = (-5 ± √489) / 4
x = 4.2783, -6.7783
x = 4.28, -6.78 (to 2 decimal places)

c)
For the box, reject x = -6.78
Hence, x = 4.28

Volume of the box
= Base area * Height
= 58 (x - 2) cm³
= 58 * (4.28 - 2) cm³
= 58 * 2.28 cm³
= 132.24 cm³

Everything looks correct in your answers, except you lost the 'x' at the beginning when you were distributing:
x(2x + 5) = 58
2x² + 5x = 58 <-- (5x, not just 5)
...

2x^2 + 5x - 58 = 0
Solutions:
x = - 5/4 - sqrt(489)/4 ≈ -6.7783
x = sqrt(489)/4 - 5/4 ≈ 4.2783

So what exactly is your question because it appears that the given answers are correct and that 3/4 is wrong?