7/2i
as you know, you can multiply both 7 and 2i by the same number and it'll stay the same. just like 1/3 and (1*3)/(3*3) are the same.
here you have to multiply both by the opposite of the irrational number. so:
7(-2i)/2i(-2i)
-14i/-4(i^2) /// now i^2=-1 remember?
-14i/4
-3.5i