60% of $90,000 is: 60/100*90,000=0.6*90,000=54,000
So, the sales associate plans $64,000 from the total income to come from sold listings .
40% of $90,000 is: 40/100*90,000=0.4*90,000=36,000
So, the sales associate plans $36,000 from the total income to come from sales made.
If the average commission from listings sold is $3,000 she must cell X=64,000/3000=21,3 ~22 listings (at least) in order to achieve her goal.