As we know that two rational numbers said to be equivalent if they are equal to each other.
HCF of $$\dfrac{-3}{5}=1$$
HCF of $$\dfrac{-27}{45}=9$$
Dividing denominator and numerator of $$\dfrac{-27}{45}$$ by $$9$$
$$\Rightarrow \dfrac{-27÷9}{45÷9}=\dfrac{-3}{5}$$
$$\Rightarrow \dfrac{-3}{5}=\dfrac{-3}{5}$$
$$\therefore \dfrac{-27}{45}=\dfrac{-3}{5}$$
Therefore, both are equivalent rational numbers.