Determine the equation of combined variation. then solve for the missing value.

x varies directly with y and inversely with z.
x = 5 when y = 10 and z = 5.
find x when y = 20 and z = 10.

its not 10 i already tried

Y=kx is the direct variation equation. Since they also want INVERSELY with z, z becomes the denominator.
Fill in the x, y and z given to find K. Then make a new equation with the variables x, y and z but plugging in the k. Once you have this new equation you can find any value for x, y or z.
10 = (5/5)* k
10= 1* k
10=k
The new equation is y = kx/z
20 = 10x/10
20 = x
Hope you understand.