Answer: When x=2 and z = 1, then the value of y =4.
Step-by-step explanation:
Given: y varies directly as x and z i.e. 
(i) , where k is the proportionality constant.
Put Y=40 ,x =5 and z = 4, then we get

Required equation:
[Put value of k in (i)]
Now put x=2 and z = 1, then we get

Hence, when x=2 and z = 1, then the value of y =4.