I would just do this
#leftCol {
width: 205px;
float: left;
margin: 0;
padding: 0;
}
#centerCol {
width: 150px;
float: left;
margin: 0;
padding-left: 10px;
}
#rightCol {
width: 250px;
float: left;
margin: 0;
padding-left: 10px;
}
/* hide center and left in mobile */
@media only screen and (max-width: 769px) {
#leftCol, #centerCol {
display: none;
}
}