I’m pretty sure it’s 2:5 hope that helps!
You need to simplify it first.

Use distribution

y=mx+b
m=slope
your slope is -4 :)
The answer is your equation does not pass though the point (1,8)
Ok, so after you do -8a+5a, you also have to do 6 -35, getting the equation
-29-3a
Let the side lenght of cube is a
voluem of cube= 0.008
a^3=0.008
a =0.2
side of lenght is 0.2