Let the amount of Tilapia bought be "t" and the amount of Salmon bought be "s"
Since Tilapia costs $3 per pound and Salmon costs $5 per pound, we can say:
Cost of Tilapia = 3t
Cost of Salmon = 5s
Their total cost = 3t + 5s
This total cost should be equal to the total budget, which is $210.
We can equate and write:
![3t+5s=210](https://img.qammunity.org/2023/formulas/mathematics/high-school/bpz6dk8fp9s0pvwyf32d91p6gi9dtd9d5b.png)