SEAMO 2027 - Paper D - SET 02 - Self-study Question 3

The quadratic equation $ax^2+bx+c=0$ has no real roots. Adam obtained roots 2 and 4 because he wrote down a wrong value of $a$. Ben obtained roots $-1$ and 4 because he wrote the sign of one term wrongly. Find $\dfrac{2b+3c}{a}$.