# How do you simplify 3i(5-4i)?

The result is $12 + 15 i$
To simplify this expression you have to multiply each term in brackets: $5$ and $- 4 i$ by $3 i$ remembering that $i \cdot i = - 1$
$3 i \left(5 - 4 i\right) = 3 i \cdot 5 - 3 i \cdot 4 i = 15 i - 12 {i}^{2} = 15 i - 12 \cdot \left(- 1\right) = 15 i + 12 = 12 + 15 i$