ΔDCQ and ΔDRB are similar triangles thus the corresponding sides of the triangles have the same proportion.
Make a comparison of the corresponding sides
plug in the numbers to the comparison above
simplify the equation

simplify 39 and 65 by dividing them by 13
Do cross multiplication
Solve the equation5x = 3(x + 18)
5x = 3x + 54
5x - 3x = 54
2x = 54
x = 54/2
x = 27
The value of x