Lets suppose k is the constant of proportionality.
z = k * x / y
when x is 16 and y is 17, z has the value 11.294117647059
11.294117647059 = k * 16/17
Multiplying 17 on both sides
11.294117647059 * 17 = k * 16
192 = k * 16
Dividing 16 on both sides
192/16 = k
k = 12
Now when x= 22, and y= 26
z = k * x/y
z = 12 * 22 / 26
z = 10.1538461538 : Answer
Hope it will help :)