help !

We found the first answer but we don’t know for the second part. The third part talks about a cube and it has three differents sides… is it possible ? A cube has all the same sides.
So we need your help for the second part ^^

First part :
x is the longer
y is the wide

x*y=300

4x=y

x*4x=300

5x=300

x=300/5

x=60

60*y=300

y=300/60=5 But 60 isn’t four times longer than 5…

Third part :

We know that y=7

So x= 7/2=3.5 and z=3.5*3=10.5

x*y*z=7*3.5*10.5= 257.25m3

bye