Isolate the x. Note the equal sign. What you do to one side, you do to the other.
Cross multiply
(4/9)(9)(36) = (x/36)(36)(9)
(4)(36) = (x)(9)
Simplify
144 = 9x
Isolate the x. Divide 9 from both sides
144/9 = 9x/9
x = 144/9
x = 16
16 is your answer
hope this helps