The variable z is directly proportional to x. when x is 15, z has the value 45.
what is the value of z when x = 23

Hello!

If variable Z is directly proportional to X, this means that the value of X increases a certain amount when Z increases. The same will apply to decreasing of either variable.

If Z = 45, X = 15. This means Z is 3 times as much as X.
X is currently 23. We can now figure out for Z.

Since Z is 3 times as much as X, multiply 23 by 3.
23 * 3 = 69

The value of Z is 69 when X is 23.

I hope this helps!