I am assuming you mean 5 / (3 + i)
Multiply top and bottom of the fraction by the complement of 3+i ( which is 3-i)
= 5(3 - i) / (3 + i)(3 - i)
= 15 - 5i / (9 - 3i + 3i - i^2) [Note - i^2 = + 1)
= (15 - 5i) / ( 9 + 1)
= ( 15 - 5i ) 10
= 1.5 - 0.5i answer
