Simplify by first factorising the numerator and denominator:

(x^2-x-12)/(〖5x〗^2+20x) ÷ (x+3)/15

To simplify the expression, let's first factorize the numerator and denominator separately.

Factorizing the numerator (x^2 - x - 12):
The numerator can be factored as (x - 4)(x + 3).

Factorizing the denominator (5x^2 + 20x):
The denominator can be factored as 5x(x + 4).

Now, let's rewrite the expression with the factored forms:

[(x - 4)(x + 3)] / [5x(x + 4)] ÷ (x + 3) / 15

Next, we can simplify the expression by canceling out common factors in the numerator and denominator:

[(x - 4)(x + 3)] / [5x(x + 4)] * [15 / (x + 3)]

After canceling out the common factor (x + 3) in the numerator and denominator, we get:

[(x - 4) * 15] / [5x * 1]

Therefore, the simplified expression is:

(15x - 60) / (5x)

or

3(x - 4) / x