.g div:nth-child(1) {
  width: 100px;
}

.g div:nth-child(2) {
  width: calc((99.99% - (100px + (30px * 1))) * 1/2 - (30px - 30px * 1/2));
}

.g div:nth-child(3) {
  width: calc((99.99% - (100px + (30px * 1))) * 1/2 - (30px - 30px * 1/2));
}