To find x:z, we need to find the ratio between x and z.

Given that x:y = 7:9, we can rewrite this as x/y = 7/9.

Similarly, given that y:z = 15:7, we can rewrite this as y/z = 15/7.

To find x:z, we can multiply the two ratios:

(x/y) * (y/z) = (7/9) * (15/7)

The y’s cancel out, leaving us with:

x/z = (7/9) * (15/7)

Simplifying this expression, we get:

x/z = 105/63

x/z = 5/3

Therefore, x:z = 5:3.