(6 + 5i)(4 + 7i) = 24 + 42i + 20i + 35i²
= 35i² + 62i + 24
The product of 6+5i and 4+7i is 35i² + 62i + 24.
You have to subtract 4 from 7 and then add 5 and 3 then add 8 and 2 then multiply 10 with 3 to get 30.
I hope that helps, coz l've done what i know
It means without preparation, extemporaneously.