Find I_x in the network.
Image from: Irwin, J. David., and R. M. Nelms. Basic Engineering Circuit Analysis, Tenth Edition. N.p.: John Wiley & Sons, 2010.
We can figure out I_x by writing Kirchhoff’s current law for the whole circuit loop. (Forgot Kirchhoff’s current law?)
This question can be found in Basic Engineering Circuit Analysis, 10th edition, chapter 2, question 2.14.