Perform the indicated operations & simplify.

Add: (810i)+(15+6i)\displaystyle {\left({8}-{10}{i}\right)}+{\left({15}+{6}{i}\right)}
sum =  

Subtract: (810i)(15+6i)\displaystyle {\left({8}-{10}{i}\right)}-{\left({15}+{6}{i}\right)}
difference =