Answer:
student a answered correctly
Step-by-step explanation:
student b didn't multiply the crossproducts
Volume cube=side^3
side=6/7
volume=(6/7)^3
remember
(a/b)^c=(a^c)/(b^c)
(6/7)^3=(6^3)/(7^3)=216/343
the volume is 216/343 cubic units
3x^4 becomes 3(3x)^4=3*3^4*x^4
y^2 becomes (3y)^2=3^2y²
the new z=3² the old z, so b is correct.