func: function buyPack(uint256 _amountOfTokens) public payable {
          require(packsToWei[_amountOfTokens] > 0);
          require(msg.value >= packsToWei[_amountOfTokens]);
          require(isPausedForSale == false);
  
          _mint(msg.sender, _amountOfTokens * 1 ether);
          (msg.sender).transfer(msg.value.sub(packsToWei[_amountOfTokens]));
  
          totalEarnings = totalEarnings.add(packsToWei[_amountOfTokens]);
          totalEarningsForPackSale = totalEarningsForPackSale.add(packsToWei[_amountOfTokens]);
  
          emit PackBought(msg.sender, _amountOfTokens, packsToWei[_amountOfTokens]);
      }