Find BD. NO LINKS ALLOWED PLEASE.
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Step-by-step explanation:

You have an angle bisector in AD. That means the sides are in proportion to to BD and DC

It's much easier just to look at the proportion.

AB / BD = AC/DC

18 / (3x - 3) = 15/(x + 5)              Cross multiply

18*(x + 5) = 15 (3x - 3)                Remove the brackets

18x + 90 = 45x - 45                  Switch the sides.

45x - 45 = 18x + 90                  Subtract 18x from both sides

-18x           -18x

27x - 45 = 90                           Add 45 to both sides

      +45    45

27x = 135

x = 5

But that's not the answer (even though it is correct). You want BD

BD = 3x - 3

BD = 3*5 - 3

BD = 15 - 3

BD = 12