Question 704759
If 150kg is 3%, then the 97% water needed is (150/3)97 kg, or 4850kg,
but you should not add water to concentrated acid; you are always supposed to add the acid to the water. 
As you start adding the mixture gets hot, and a little acid gets much hotter than a lot of water. As it starts boiling, hot a I'd splashes up (not to mention the fuming), and it is dangerous.
KMST
a chemist