The number of watches that just be sold is 90 and the profit is -356400.
From the information given, the equation is given as:
P = −50x² + 550x − 900
P = -5x² + 55x - 90
= -5x² + 45x + 10x - 90
= -5x(x - 9) + 10(x - 9)
= (-5x + 10)(x - 9)
x - 9 = 0
x = 0 + 9 = 9
The watches that must be sold will be (9 × 10) = 90
The profit will be:
P = −50x² + 550x − 900
P = -50(90)² + 550(90) - 900
P = -405000 + 49500 - 900
P = -356400
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