Question

How do you find the value for x in the problem?

Answer 1

Make use of the fact that side lengths in similar triangles are proportional.
.. 30/18 = (20 +x)/20
.. 20*(30/18) -20 = x . . . . multiply by 20, subtract 20
.. 33 1/3 -20 = x . . . . . . . . evaluate the product
.. 13 1/3 = x