Final answer:
Given the direct and inverse proportionality, the constant of proportionality was found to be 5.
Subsequently, y was calculated as 10 when x is 18 and z is 9.
Step-by-step explanation:
If y varies directly as x and inversely with z, we can represent this relationship with the equation y = k(x/z), where k is the constant of proportionality.
Given that y=25 when x=10 and z=2, we can find k by substituting these values into the equation:
25 = k(10/2), thus, k = 5.
To find y when x=18 and z=9, we substitute these values and our constant k into the original equation:
y = 5(18/9),
y = 5(2),
y = 10.
Therefore, y is 10 when x=18 and z=9.