a) y = 9216
b) y = 360
Since x and y vary directly, y and x are directly related and can be expressed as y = kx. where k is a constant
y will increase as x increases. y will also decrease as x decreases.
I used k1 and k2 to separate the two questions and avoid confusion but using the constant k is fine.
a) For part a, you can substitute y = kx with the values of y and x.
![1024 = k1 * 9](https://img.qammunity.org/2023/formulas/mathematics/high-school/ne64e4igt09af52ur3poe8yyvo59hfii2h.png)
Hence, we can find the constant k1
![k1 = (1024)/(9)](https://img.qammunity.org/2023/formulas/mathematics/high-school/suo3hijhi23psqitoptx38g5lxzoysacfu.png)
Now, we can plug in the values into the original equation and obtain the new equation
![y = (1024)/(9) x](https://img.qammunity.org/2023/formulas/mathematics/high-school/1w8wlxzlg8q77y0bsh8azhz6vqrscnniix.png)
We can now solve part a by plugging in 81 into the value of x.
![y = (1024)/(9) * 81 = 9216](https://img.qammunity.org/2023/formulas/mathematics/high-school/awf0r5dron5xj09rtt7ul9l7e2l5ike6iv.png)
b) Like part a, we can use the same method to find y for part b.
substitute y = kx with the values of y and x.
![72 = k2 * (1)/(2)](https://img.qammunity.org/2023/formulas/mathematics/high-school/kjzjdq78d21necjduot8elyj59jwd6u7n7.png)
Hence, we can find the constant k2
![k2 = 72 / (1)/(2) = 144](https://img.qammunity.org/2023/formulas/mathematics/high-school/okwlfdhiqsud8jwvyxdtawieose8i6c2yo.png)
Now, we can plug in the values into the original equation and obtain the new equation
![y = 144x](https://img.qammunity.org/2023/formulas/mathematics/high-school/7ye8lh4cfqvycq92fsy5yyeps9w7gbp5ck.png)
We can now solve part a by plugging in 5/2 into the value of x.
![y = 144 * (5)/(2) = 360](https://img.qammunity.org/2023/formulas/mathematics/high-school/o0fz14eut98vuvaj6t84je6snornvw9bon.png)