Question 57996
using the foil method multiply out the question the first of term a to the two terms in b, and the second term in a by the 2 terms in b.

so you get

(5)(3)+(5)(-7i)+(4i)(3)+(4i)(7i)
or
15-35i+12i+28i^2

combine like terms

28i^2-(23i)+15