### Instruction: If $a @ b$ is defined as $a @ b$ = $3a - 3b$, what is the value of $3 @ 5$?### Response: To evaluate $3 @ 5$, I need to plug in $a = 3$ and $b = 5$ into the definition of $a @ b$.
So I get $3 @ 5$ = $3(3) - 3(5)$.
Simplifying, I get $9 - 15$.
This is $-6$.