Morning all,

Not sure if i'm making a double post here not, but got an assignment back, and seems i've gone wrong on just one of the answers. Therefore, I was hoping someone could help me out

Gut feeling, is that i'm approaching the question wrong, but we will see:

Question:From a rectangular sheet of metal measuring

120 mmby75 mmequal squares of sideare cut from each of the corners. The remaining flaps are then folded upwards to form an open box. Show that the volume of the box is given by:x

V = 9000x– 390x^{2}+ 4x^{3}

Find the value ofsuch that the volume is a maximum.x

Answer:I wasn't entirely sure how to approach it, and ended up with something like this (see image):

Thanks in advance for any help