Alright, lets get started.
Suppose total values of drug Alejandro sold = x
He earns a 12% commission of the total sales of the statins that he sells to hospitals.
It means he get 12 % of commission of his total sale x.
So, the commission he get 
commission he get 
commission he get 
As per given in question, he earned $60,000 in commission.

Dividing both sides with 0.12


It means his total sales is $ 500000. : Answer
Hope it will help :)