Question 6203
Let us assume that solution A required is 'x' litres & solution B required is 'y' litres.
we can see that x+y=60---------(1)
now 10% acid =10*60/100 litres=6 litres.
now the tricky part....
 12% 0f 'x' =12*x/100 & 4% of 'y'=4*y/100 ......(all in litres)
  thus we get 12*x/100+4*y/100=6
             =>3*x/25+y/25=6
             =>3*x+y=150--------(2)
 solving the above simultaneous equations numbered (1)& (2)......
  we get
  x=45  &  y=15
 hence solution A required is 45 litres & solution B required is 15 litres.