First, we are going to convert your sales commissions from percentages to decimals. To do that we are going to divide each one by a 100%:
5%=

8%=

Next, we know for our problem that your sales commission will be 5% if you sell up to $100,000. So, if

represents the amount that you sell each month, the first equation of our piece wise function will be

.
Similarly, we know that your sales commission will be 8% if you sell more than $100,000; therefore, the second equation of our piecewise function will be

.
Now, lets put all together to create our picewise function: