I think it would be c if it were a greater rate I don't know if i am right I'll check back with you guys on the answer
So since they are similar
AC/BC=CD/CE
so
(66-x)/30=(x+4)/5
times both sides by 5
(66-x)/6=x+4
times both sides by 6
66-x=6(x+4)
distribute
66-x=6x+24
add x to both sides
66=7x+24
minus 24 from both sides
42=7x
divide both sides by 7
6=x
x=6 units
this is how I would solve this problem, hope it helps