#### Answer

$$ 11-41i$$

#### Work Step by Step

With imaginary numbers, we foil like normal. This means that we multiply the first terms in each factor by each other. Then, we multiply the two outer terms by each other. Next, we multiply the two inner terms. Finally, we multiply the two terms that have yet to be multiplied by each other. Recall, whenever we multiply $i$ by itself, the result is $-1$. Thus:
$$21-10-6i-35i \\ 11-41i$$