-3i(5-4i)=0

Solution for -3i(5-4i)=0 equation:

-3i(5-4i)=0

We add all the numbers together, and all the variables

-3i(-4i+5)=0

We multiply parentheses

12i^2-15i=0

a = 12; b = -15; c = 0;
Δ = b2-4ac
Δ = -152-4·12·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$i_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$i_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$i_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-15}{2*12}=\frac{0}{24}
=0
$
$i_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+15}{2*12}=\frac{30}{24}
=1+1/4
$