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 4% of the panels from plant b were defective. how many panels did plant b produce, if the two plants together produced 1920 defective panels?

Suppose plant B made x panels, plant A made 4x panels:
Given that 5% of panels from plant A were defective, the number of panels which were not defective were:
95/100*4x=3.8x panels
Given that 4%of panels from plant B were defective, the number of panels which were not defective was:
96/100*x=0.96x
the total number of panels made was 1920.
Thus the number of panels each plant made will be given by:
0.96x+3.8x=1920
solving for x we get:
4.76x=1920
x=1920/4.76
x=403
therefore, plant B made 403 panels

The answer would be 315 because you need to subtract

What do you mean by that?