Multiply (9+5i)(6+i)?

(9 + 5i)(6 + i)
= 49 + 39i

54 + 9 i + 30 i - 5 = 49 + 39 i

(9+5i)(6+i)
polynomial multiplication:
9(6+i) + 5i(6+i)
54 + 9i + 30i + 5i² : i² = -1
54 - 5 + 39i
49 + 39i

Expanding out the brackets

(9 + 5i) (6 + i)

9 x 6 = 54
9 x i = 9i
5i x 6 = 30i
5i x i = 5i²

= 54+9i+30i+5i²
= 54 + 39i + 5i²

54 + 39i - 5
49 + 39i

i^2 = -1