Answer:
![Brother = 105 + 3d](https://img.qammunity.org/2022/formulas/mathematics/high-school/8c3hevfcarlld469d7aq1zppzmnjml8i9l.png)
Explanation:
Given
![Drone = d](https://img.qammunity.org/2022/formulas/mathematics/high-school/81rdjenub7uf939k2k5bsvo0n1yd5y05f5.png)
Friend = $35 more expensive than yours.
Brother = 3 * as much as your friend
Required
Write an expression for the cost of your brother's drone
I'll solve by analysing the question one sentence after the other
You:
![Drone = d](https://img.qammunity.org/2022/formulas/mathematics/high-school/81rdjenub7uf939k2k5bsvo0n1yd5y05f5.png)
Your friend:
Friend = $35 more expensive than yours.
This means
![Friend = 35 + You](https://img.qammunity.org/2022/formulas/mathematics/high-school/cmatg8630r8hupuhpkpwtv1a2qrb06nxyx.png)
Substitute d for You
![Friend = 35 + d](https://img.qammunity.org/2022/formulas/mathematics/high-school/xe74t7709gpr6pcy0t1965hzi2xx0ncvam.png)
Your brother:
Brother = 3 * as much as your friend
This means:
![Brother = 3 * Friend](https://img.qammunity.org/2022/formulas/mathematics/high-school/k7seljoamwj6r3tqb6ep5ns5mwot4qdxuq.png)
Substitute 35 + d for Friend
![Brother = 3 * (35 + d)](https://img.qammunity.org/2022/formulas/mathematics/high-school/7lvvii8tcqi2v80oov2ntx4ar29yiebz94.png)
Open bracket
![Brother = 3 * 35 + 3*d](https://img.qammunity.org/2022/formulas/mathematics/high-school/c9mutnf0l97eksyvbkl1ttwt9bdsl07jbd.png)
![Brother = 105 + 3d](https://img.qammunity.org/2022/formulas/mathematics/high-school/8c3hevfcarlld469d7aq1zppzmnjml8i9l.png)