@seema what ur saying is true for value added by a single firm but not for gdp....
in this particular question ..for gdp u require the sum of value added by all firms...we just need to add first value added by x nd y....nd z also.....z is also a firm in the economy and what it is selling is a final good for it...
so answers acc to me shud be"
12. 16.5
13. 18
14. 150
15. 20%
Should answer 12 be 16.5 ? pxqx + pyqy ... No subtraction of pzqz because it is an intermediate good (check page 22 Mankiw Macroeconomics..)
And thus, answer 13 is 18 (6*1+6*2)
14 - 150 (6*1.5 +18/18 into 100)
15 - 20 % (growth is 18-15/15 into 100)
am----- they are intermediate products for x and y so we subtract them.....but they are final products of firm z so we add them....so in net terms only the sales of x nd y get counted....both of us are saying same thing albeit with a different perspective!!!!!!