If you would like to write an inequality to represent the situation, using X to represent the amount of Alicia's paycheck, you can calculate this using the following steps:
X ... the amount of Alicia's paycheck
X/2 - $42.15 >= $20
X/2 >= $20 + $42.15
X/2 >= $62.15 /*2
X >= $62.15 * 2
X >= $124.3
The correct result would be X >= $124.3.