x = 3y ------------------(1)
y = 4z ---------------------(2)Given
x = 3y
= 3*(4z) [ from (2) , y = 4z ]
x = 12z ----------------------------(3)
If x = 30,
substitute in (1)
3y = x
3y = 30
y = 30/ 3
y = 10
substitute y = 10 in equation (2)
4z = y
4z = 10
z = 10 / 4
z = 5 /2