Question

If f(x) = 3x +9 x when f(x) = 30

Answer 1

Answer:

$x=5/2$

Step-by-step explanation:

When $f(x)=30$, we have $3x+9x=30$.

Combining like terms on the right side, we have $12x=30$.

Finally, dividing by $12$ we get $x=30/12$.

We note that $30=6*5$ and $12=6*2$, so $30/12=5/2$.

So, $\boxed{x=5/2}$ and we're done!