Using the Angle Bisector Theorem solve for x.
The "Angle Bisector" Theorem says that an angle bisector of a triangle will divide the opposite side into two segments that are proportional to the other two sides of the triangle.
As, we see the figure, AD bisects angle A
So, Applying Angle Bisector theorem, we get,



15 divide by 3 gives 5
So, we have
5=

To get rid of fractions let us multiply by 5 on both sides
5*5=

25=

25=4x+1
To solve for x, let us subtract 1 from both sides
25-1=4x+1-1
24=4x+0
Or, 4x=24
To solve for x, let us divide by 4 on both sides

x=6
Answer: x=6