Question

check my answer!

Answer 1

@xapproachesinfinity

Answer 2

@phi any help?

Answer 3

varies directly means z= kx
varies indirectly means z = k/y
if you have both types, you write
\[ z = k \frac{x}{y} \]
we use the info to find k
x=6, y=2, z=15 in the formula:
\[ 15= k \frac{6}{2} \\ 15= k 3 \\ 15/3 = k \\k=5\]

Answer 4

now use k=5 to write the variation :
\[ z = 5 \frac{x}{y} \]
and use x=4, y=9 in that formula
you will get
z= 20/9
which is what you chose