The minimum number of total variables required to convert the above code segment to static single assignment form is?

Consider the following code segment.

x = u - t;
y = x * v;
x = y + w;
y = t - z;
y = x * y; 

The minimum number of total variables required to convert the above code segment to static single assignment form is_________.

I need a thorough explanation on how to deal with such questions.... 

Thank you..

2Comments
Sumit Verma @sumitkgp
21 Jun 2017 12:53 am
Niket Gangwar @niket151194
21 Jun 2017 12:59 am

thank you Sir....