Let us assume the number of panels produced by Plant A = z
Let us assume the number of panels produced by Plant B = y
Then
x = 3y
0.03x + 0.04y = 1300
Multiplying both sides of the second equation by 100, we get
3x + 4y = 130000
Putting the value of x from the first equation in the second equation, we get
3x + 4y = 130000
3(3y) + 4y = 130000
13y = 130000
y = 10000
Then
x = 3 * 10000
= 30000
From the above deduction, we can conclude that the number of panels made by Plant A is 30000.
