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Number of biology textbooks sold: x
Number of math textbooks sold: x - 45
x + x - 45 = 389
2x - 45 = 389
2x = 434
x = 217
Number of biology textbooks sold: 217
Number of math textbooks sold: 217 - 45 = 172
So, 217 biology textbooks and 172 math textbooks were sold.