How to solve this percent mixture problem?

Question

Hello, I was able to solve the percent mix problem before this one, but this just has me stumped for some reason. I'm having trouble understanding how to step up mixture equations.

 

Two factory plants are making TV panels. Yesterday, Plant A produced 4 times as many panels as Plant B. Five percent of the panels from Plant A and 2% of the panels from Plant B were defective. How many panels did Plant B produce, if the two plants together produced 2640 defective panels?

Answer 1

B produced x number of panels

A produced 4x number of panels

5%(4x)+2%(x)=2640

0.2x+0.02x=2640

0.22x=2640

22x=264,000

x=264,000/22

x=12,000 panels produced by plant B

plant A produced 48,000 panels

5%*48,000+2%*12,000=2400+240=2640