Over the last 3 years, salesperson a has earned twice as much as salesper b who in turn has averaged 50% more than salesper c. the 3 combined to make $220,000 ver 3 years. how much did salesper b earn on average?

A has earned twice as much as B so: A=2B
B has averaged 50% more than C so: B=C+0.5C
Combined is 220K, So A+B+C=220,000

The last equation can be re-written as:
2B+1.5C+C=220K
AND since A=2B, it can be rewritten again as:
3C+1.5C+C=220K

Now you can get C finally, since B=1.5C you can get B, then to get the average, just divide that by 3 (years) and you should be done.
So B = 60000 for 3 years