If all enemies have the same exp that you get after killing them you can add a multiplier like this
Have not coded/created a game for some time so am sorry if code does not work
Int enemyexp= 12× expmultiplier;
// for example int enemyexp = 12×1.2; which would make enemyexp= 14,4. Which would make it 14.
Or you can make it so you can do plus 5 or plus 10 to exp (read previous post)
In that case
Int enemyexp = 12 + extraexp
//extra exp would have to be a global int to work on all scripts,
//this woukd in theory make it so int enemyexp= 12+5 which is 17