Hi,
Whether this system is causal or not depends on your ROC or region of convergence.
If you want this system to be causal then take a ROC |z|>0.5 and you will get
h[n]=0.18*{sin(0.7n)*(0.5)^n }u[n].
With this h[n] the system is causal.
For more discussion on Z-transform illustrating the concept of causality, you can download the book at this site.
It contains an excellent chapter about Z-transform
it is simple.a causal system is a system whose output depends only on present and past inputs and not future inputs.just equate this to y(z /x(z) and find the inverse z transform .then u will find that the system specified is a causal system.in short the response of the system should be zero for n<0.where n is the time index.
you can now that takin a review in any control book like the kuo , ogatta or the dorf, or if you wanna go deeper you can see any signal and systen book like the haykin or amdabar.