If 3x=8y, 12y=7z and kz=72x, then what is the value of k

show your work

k*z = 72*x
so k = 72 * (x / z) (1)

you can express both x and z in y:

3x =8y 7z = 12y
so x = 8/3 * y (2) so z = 12/7 * y (3)

Substitute (2) and (3) in (1) gives you;

k = 72 * ( 8/3 * y )/(12/7 * y)
k = 72 * (14/9) * y/y = 1008/9 * 1 = 112

there is only one answer for k. you have to do more than one equation of plugging in whatever you want to figure it out.
think about it.
i can make x=8/3 in 3x=8y which would make y=1
12(1)= 7(12/7)
k(12/7)=72(8/3)
k=112
or i can make x=8 and y=3 in 3x=8y
so 12(3)=7(5 and 1/7)
k(5 and 1/7) = 72(8)
k=112