If you would like to know what is the appropriate simplified form and restriction for the variable, you can calculate this using the following steps:
(3x^2 + 9x) / ( x^2 - 2x - 15) = (3x * (x + 3)) / ((x - 5) * (x + 3)) = 3x / (x - 5)
The simplified form is 3x / (x - 5) and the restriction for the variable would be x ≠ 5 and x ≠ -3.