it is right tail test here significant level a =0.05 1-a=1-0.05= 0.95 now use Z table ,corresponding value of Z from table (corrospnding to =0.95)) =1.645 so we have critical value of Z Z a = 1.645 as critical value of Z =1.645 so Decision Rule is - Reject null hypothesis if test statistics Z Greater than 1.645