xvxvxv

so what can I do ! 

Can I download the book from here ?? 

for question 20 ... 

I think that they should say in the question that the weight is in Equilibrium   right ~ ! 

thank you heureka

Now its very clear .. thank you david 

but what about 6 , 7 and 8 

are there correct 

fine .. my last question .. why you put the heights 3 m !