.
(a) = 5 -3i.
(b) = 5*5 +2*5*3i- 9i^2 = 25 + 30i + 9 = 34 + 30i.
On complex numbers, read my introductory lessons
- Complex numbers and arithmetical operations on them
- Complex plane
- Addition and subtraction of complex numbers in complex plane
- Multiplication and division of complex numbers in complex plane
in this site.