Question 1069197
This is just to get you started.
For the zinc, total new mass will become  x+y+240 kg.
Amount of zinc in the new alloy is  0.35*240+x, and concentration wanted is  40%, or 0.4.


{{{(0.35*240+x)/(x+y+240)=0.40}}}, using decimal fractions instead of percents.


Multiply left and right by  {{{x+y+240}}}:


{{{0.35*240+x=0.40(x+y+240)}}}



Now just do the same thing for the lead.



Once you have the two equations, simplify them and solve the system for x and y.



Simplified system to solve can become  {{{system(3x-2y=60,-x+24y=60)}}}.


RESULTS:
{{{system(x=22&2/7,y=3&4/7)}}}