Solved

function solve(t1, t2)
  local result = t1;
  for i = 1, #t2 do
    result[#result + 1] = t2[i];
  end
  return result;
end

function printTable(title, tbl)
  print(title)
  for i = 1, #tbl do
    io.write(tbl[i] .. " ");
  end
  print()
end

table1 = {4, 7, 2, 3, 1};
table2 = {8, 5, 7, 4};

tableResult = solve(table1, table2);

printTable("First table", table1)
printTable("Second table", table2)
printTable("Result", tableResult)


--[[
The output
  First table
  4 7 2 3 1 8 5 7 4
  Second table
  8 5 7 4
  Result
  4 7 2 3 1 8 5 7 4
]]