Explanation:
x = number of par one balls ordered.
y = number of supra balls ordered.
2.10×x = 1.00×y + 330
2.1x = y + 330
y = 2.1x - 330
x = y (equal number was ordered).
so,
x = 2.1x - 330
0 = 1.1x - 330
330 = 1.1x
x = 330/1.1 = 300
y = x = 300
1 dozen = 12 pieces
so,
300/12 = 25 dozens
25 dozens balls were ordered from each brand.